Commands in PRs to build release candidates

[mempirate]

Context

We can use the issue_comment trigger with a predefined command (such as /build bolt-sidecar:v0.5.0-alpha.rc1) to build images in CI on our self-hosted runners on-demand.

Considerations

• Only allow core contributors to run this command
• Would be nice to get a comment from github actions when the build is completed

Template from ChatGPT:

(Needs security checks)

# .github/workflows/docker-build-on-comment.yml
name: Build Docker Image on Comment

on:
  issue_comment:
    types: [created]

jobs:
  build:
    if: |
      github.event.issue.pull_request != null &&
      startsWith(github.event.comment.body, '/build ')
    runs-on: ubuntu-latest

    steps:
      - name: Extract subdirectory and tag from comment
        id: extract
        run: |
          echo "Comment: ${{ github.event.comment.body }}"
          if [[ "${{ github.event.comment.body }}" =~ ^/build[[:space:]]+([^:]+):(.+)$ ]]; then
            echo "subdir=${BASH_REMATCH[1]}" >> $GITHUB_ENV
            echo "tag=${BASH_REMATCH[2]}" >> $GITHUB_ENV
          else
            echo "Comment does not match the expected pattern."
            exit 1
          fi

      - name: Checkout PR code
        uses: actions/checkout@v3
        with:
          ref: ${{ github.event.issue.pull_request.head.ref }}

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v2

      - name: Log in to GitHub Container Registry
        uses: docker/login-action@v2
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Build and push Docker image
        uses: docker/build-push-action@v4
        with:
          context: ./${{ env.subdir }}
          push: true
          tags: ghcr.io/${{ github.repository_owner }}/${{ env.subdir }}:${{ env.tag }}

      - name: Post comment on PR
        uses: thollander/actions-comment-pull-request@v1
        with:
          message: |
            The Docker image has been successfully built and pushed to GHCR.
            Image: `ghcr.io/${{ github.repository_owner }}/${{ env.subdir }}:${{ env.tag }}`
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}