Extract pool/signing variables into reusable template (#2032)

Move pool/image configuration and MicroBuild signing variables from
dotnet/common.yml into a new pool-and-signing.yml template.

dotnet/common.yml currently bundles these shared variables together with
the DotNet-Docker-Common-2 variable group, which forces downstream repos
(e.g. go-images) to copy-paste ~80 lines of pool and signing config
rather than importing dotnet/common.yml directly.

By extracting pool-and-signing.yml, downstream repos can import just the
shared variables without pulling in dotnet-specific variable groups or
re-importing base templates that would override their customizations.

See
https://github.com/microsoft/go-images/blob/microsoft/main/eng/pipeline/variables/go-common.yml
as an example of how much downstream duplication we need right now
simply because we can't import the `DotNet-Docker-Common-2` variable
group from `eng/docker-tools/templates/variables/dotnet/common.yml`

---------

Co-authored-by: Logan Bussell <loganbussell@microsoft.com>

Author: gdams

eng/docker-tools/templates/variables/dnceng-build-pools.yml

@@ -0,0 +1,58 @@
+# Build pool and image variables for dnceng pipelines.
+# Reference this template in pipelines that run in the dnceng or dnceng-public Azure DevOps orgs.
+
+variables:
+- name: linuxAmd64InternalPoolImage
+  value: build.azurelinux.3.amd64
+- name: linuxAmd64PublicPoolImage
+  value: build.azurelinux.3.amd64.open
+- name: linuxAmd64PublicPoolName
+  value: NetCore-Public
+- name: linuxAmd64InternalPoolName
+  value: NetCore1ESPool-Internal
+
+- name: linuxArm64PublicPoolImage
+  value: build.azurelinux.3.arm64.open
+- name: linuxArm64InternalPoolImage
+  value: build.azurelinux.3.arm64
+- name: linuxArm64PublicPoolName
+  value: Docker-Linux-Arm-Public
+- name: linuxArm64InternalPoolName
+  value: Docker-Linux-Arm-Internal
+
+- name: linuxArm32PublicPoolImage
+  value: build.azurelinux.3.arm64.open
+- name: linuxArm32InternalPoolImage
+  value: build.azurelinux.3.arm64
+- name: linuxArm32PublicPoolName
+  value: Docker-Linux-Arm-Public
+- name: linuxArm32InternalPoolName
+  value: Docker-Linux-Arm-Internal
+
+- name: windowsServer2016PublicPoolImage
+  value: Server2016-NESDockerBuilds
+- name: windowsServer2016InternalPoolImage
+  value: Server2016-NESDockerBuilds-1ESPT
+- name: windowsServer2016PoolName
+  value: Docker-2016-${{ variables['System.TeamProject'] }}
+
+- name: windowsServer2019PublicPoolImage
+  value: Server2019-1809-NESDockerBuilds
+- name: windowsServer2019InternalPoolImage
+  value: Server2019-1809-NESDockerBuilds-1ESPT
+- name: windowsServer2019PoolName
+  value: Docker-1809-${{ variables['System.TeamProject'] }}
+
+- name: windowsServer2022PublicPoolImage
+  value: Server2022-NESDockerBuilds
+- name: windowsServer2022InternalPoolImage
+  value: Server2022-NESDockerBuilds-1ESPT
+- name: windowsServer2022PoolName
+  value: Docker-2022-${{ variables['System.TeamProject'] }}
+
+- name: windowsServer2025PublicPoolImage
+  value: Server2025-NESDockerBuilds
+- name: windowsServer2025InternalPoolImage
+  value: Server2025-NESDockerBuilds-1ESPT
+- name: windowsServer2025PoolName
+  value: Docker-2025-${{ variables['System.TeamProject'] }}

eng/docker-tools/templates/variables/dnceng-project-names.yml

@@ -0,0 +1,8 @@
+# Azure DevOps project name variables for dnceng pipelines.
+# Reference this template in pipelines that run in the dnceng or dnceng-public Azure DevOps orgs.
+
+variables:
+- name: publicProjectName
+  value: public
+- name: internalProjectName
+  value: internal

eng/docker-tools/templates/variables/dnceng-signing.yml

@@ -0,0 +1,10 @@
+# MicroBuild signing variables for dnceng pipelines.
+# Reference this template in pipelines that run in the dnceng or dnceng-public Azure DevOps orgs.
+
+variables:
+- name: TeamName
+  value: DotNetCore
+- name: MicroBuildFeedSource
+  value: https://dnceng.pkgs.visualstudio.com/_packaging/MicroBuildToolset/nuget/v3/index.json
+- name: MicroBuildPluginVersion
+  value: latest

eng/docker-tools/templates/variables/dotnet/common.yml

@@ -1,10 +1,8 @@
 variables:
 - template: /eng/docker-tools/templates/variables/common.yml@self
-
-- name: publicProjectName
-  value: public
-- name: internalProjectName
-  value: internal
+- template: /eng/docker-tools/templates/variables/dnceng-build-pools.yml@self
+- template: /eng/docker-tools/templates/variables/dnceng-signing.yml@self
+- template: /eng/docker-tools/templates/variables/dnceng-project-names.yml@self
 
 # $(dockerHubRegistryCreds) is needed by the copy-base-images step in
 # eng/docker-tools/templates/stages/build-and-test.yml#L73-L78, even during a dry-run.
@@ -13,70 +11,4 @@ variables:
 - name: dockerHubRegistryCreds
   value: --registry-creds 'docker.io=placeholder;placeholder'
 
-- name: linuxAmd64InternalPoolImage
-  value: build.azurelinux.3.amd64
-- name: linuxAmd64PublicPoolImage
-  value: build.azurelinux.3.amd64.open
-- name: linuxAmd64PublicPoolName
-  value: NetCore-Public
-- name: linuxAmd64InternalPoolName
-  value: NetCore1ESPool-Internal
-
-- name: linuxArm64PublicPoolImage
-  value: build.azurelinux.3.arm64.open
-- name: linuxArm64InternalPoolImage
-  value: build.azurelinux.3.arm64
-- name: linuxArm64PublicPoolName
-  value: Docker-Linux-Arm-Public
-- name: linuxArm64InternalPoolName
-  value: Docker-Linux-Arm-Internal
-
-- name: linuxArm32PublicPoolImage
-  value: build.azurelinux.3.arm64.open
-- name: linuxArm32InternalPoolImage
-  value: build.azurelinux.3.arm64
-- name: linuxArm32PublicPoolName
-  value: Docker-Linux-Arm-Public
-- name: linuxArm32InternalPoolName
-  value: Docker-Linux-Arm-Internal
-
-- name: windowsServer2016PublicPoolImage
-  value: Server2016-NESDockerBuilds
-- name: windowsServer2016InternalPoolImage
-  value: Server2016-NESDockerBuilds-1ESPT
-- name: windowsServer2016PoolName
-  value: Docker-2016-${{ variables['System.TeamProject'] }}
-
-- name: windowsServer2019PublicPoolImage
-  value: Server2019-1809-NESDockerBuilds
-- name: windowsServer2019InternalPoolImage
-  value: Server2019-1809-NESDockerBuilds-1ESPT
-- name: windowsServer2019PoolName
-  value: Docker-1809-${{ variables['System.TeamProject'] }}
-
-- name: windowsServer2022PublicPoolImage
-  value: Server2022-NESDockerBuilds
-- name: windowsServer2022InternalPoolImage
-  value: Server2022-NESDockerBuilds-1ESPT
-- name: windowsServer2022PoolName
-  value: Docker-2022-${{ variables['System.TeamProject'] }}
-
-- name: windowsServer2025PublicPoolImage
-  value: Server2025-NESDockerBuilds
-- name: windowsServer2025InternalPoolImage
-  value: Server2025-NESDockerBuilds-1ESPT
-- name: windowsServer2025PoolName
-  value: Docker-2025-${{ variables['System.TeamProject'] }}
-
-## Signing
-# Team name required for MicroBuild signing plugin
-- name: TeamName
-  value: DotNetCore
-# MicroBuild signing plugin feed source
-- name: MicroBuildFeedSource
-  value: https://dnceng.pkgs.visualstudio.com/_packaging/MicroBuildToolset/nuget/v3/index.json
-# MicroBuild signing plugin version
-- name: MicroBuildPluginVersion
-  value: latest
-
 - group: DotNet-Docker-Common-2