Publish docker image on push to main (#26)

* Publish docker image on push to main

These images are annotated as "latest". If desired, we can also
annotated with the short sha by adding the following line in the
tags section of the Extract metadata step:

```
type=sha,format=short,enable={{is_default_branch}}
```

This would improve traceability, but has the downside of quickly filling
up the list in:
https://github.com/eclipse-csi/pia/pkgs/container/pia/versions

Since traceability is not so important for images built off of main, I
let it out for now.

Signed-off-by: Lukas Puehringer <lukas.puehringer@eclipse-foundation.org>

* Minor fixes in publish.yml

* Remove redundant release event trigger
  ->  We already listen on tag push
* Remove unused/unneeded annotations in "Extract metadata" step.
  ->  We don't care for image annotations of type ref (branch name, pr
      number, etc.), and we don't even run on PRs

Signed-off-by: Lukas Puehringer <lukas.puehringer@eclipse-foundation.org>

---------

Signed-off-by: Lukas Puehringer <lukas.puehringer@eclipse-foundation.org>

Author: lukpueh

.github/workflows/publish.yml

@@ -4,8 +4,8 @@ on:
   push:
     tags:
       - 'v*'
-  release:
-    types: [published]
+    branches:
+      - main
   workflow_dispatch:
 
 env:
@@ -39,8 +39,6 @@ jobs:
       with:
         images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
         tags: |
-          type=ref,event=branch
-          type=ref,event=pr
           type=semver,pattern={{version}}
           type=semver,pattern={{major}}.{{minor}}
           type=semver,pattern={{major}}