Add RWX as a build provider

[robinaugh]

Hey team - Per the contributing guide, I'm seeking buyoff before opening a PR.

RWX is a cloud CI/CD platform with a growing .NET user base. I'd like to add it as a build provider under src/Cake.Common/Build/Rwx/, alongside the 14 already supported (GitHub Actions, GitLab CI, Azure Pipelines, etc.) so that Cake scripts running on RWX get the same IsLocalBuild / IsRunningOnRwx / BuildSystem.Rwx.Environment behavior they get on every other supported CI.

Detection contract

RWX exposes a documented env var contract: https://www.rwx.com/docs/environment-variables#meta-environment-variables

Proposed shape

Modeled on the existing TravisCI / GitLabCI providers — env/info only, no Commands surface for now:

src/Cake.Common/Build/Rwx/
  IRwxProvider.cs
  RwxProvider.cs
  RwxInfo.cs
  Data/RwxEnvironmentInfo.cs

Plus the usual additions to BuildProvider.cs, BuildSystem.cs, BuildSystemAliases.cs, DI registration, and unit tests modeled on the existing provider tests.

Worth flagging up front:

• IsPullRequest aggregation. RWX's current envvar contract doesn't expose a PR identifier (many runs are kicked off from the CLI before PRing), so the initial provider would not contribute to BuildSystem.IsPullRequest.
• Casing. Existing folders are inconsistent (GoCD, GitLabCI vs. MyGet). I'd go Rwx to match .NET conventions, but happy to defer.

If approved, I'll open the accompanying issue linking back to this discussion and start the PR against develop. Once that's in, we'd also document the integration in our docs at rwx.com/docs.

I appreciate the time, and I'm happy to adjust scope or shape based on what you'd prefer to see!

[devlead]

Seems like a reasonable addition, do they offer a OSS/Free/Self-hosted tier we can use for integration tests to verify?

[robinaugh]

Hey there @devlead - we can definitely set cake up with essentially endless credits for exercising the RWX integration tests, and then run that integration test on merge to main/develop/hotfix like you already do for other CI providers.

I've got the local branch set up on my end, which will include the YML definition, and I'll create an RWX org for cake-build. I'll want to add at least one maintainer email address as an admin on that org, to make sure you have direct access. Feel free to send that email to me at jason-at-rwx.com if it's not publicly available. Thanks!

[devlead]

@robinaugh thanks for the offer, email sent👍

[robinaugh]

I've opened #4836, thanks!