Add the ability to publish container for specific commit sha (#799)

For debugging purposes we need to be able to deploy a specific commit as
observer or manifest server without having to cut a release or even
merge to `main`.

.github/workflows/publish-ghcr.yml

@@ -11,14 +11,19 @@ on:
       types:
         - completed
   pull_request:
+  workflow_dispatch:
+    inputs:
+      sha:
+        description: 'Commit SHA to publish'
+        required: true
 
 jobs:
   prepare-checkout:
     if: github.event_name != 'workflow_run' || github.event.workflow_run.conclusion == 'success'
     name: Prepare ref
     runs-on: ubuntu-latest
     outputs:
-      ref: ${{ github.event_name != 'workflow_run' && github.ref || steps.releaser.outputs.version }}
+      ref: ${{ github.event_name == 'workflow_dispatch' && github.event.inputs.sha || github.event_name != 'workflow_run' && github.ref || steps.releaser.outputs.version }}
     steps:
       - name: Get version tag from releaser
         id: releaser