GitHub: Use podman/buildah and merge workflows (centos)

Let's start with CentOS images only to see if this works.

- Use podman & buildah Actions instead of Docker ones
- Use a single GitHub Action workflow for PR and main branch builds

See: #46

.github/workflows/centos.yaml

@@ -3,6 +3,9 @@ name: "CentOS: Build and push toolbx images"
 permissions: read-all
 
 on:
+  pull_request:
+    branches:
+      - main
   push:
     branches:
       - main
@@ -12,54 +15,63 @@ on:
   schedule:
     - cron:  '0 0 * * MON'
 
-# Prevent multiple workflow runs from racing
-concurrency: ${{ github.workflow }}
-
 env:
   distro: 'centos'
   distro_pretty: 'CentOS'
   latest_release: 'stream9'
+  registry: 'quay.io/toolbx-images'
+
+# Prevent multiple workflow runs from racing to ensure that pushes are made
+# sequentialy for the main branch. Also cancel in progress workflow runs for
+# pull requests only.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
-  build-and-push-images:
+  build-push-images:
     strategy:
       matrix:
         release: ['stream8', 'stream9']
 
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@v2
+      - name: Set up QEMU for multi-arch builds
+        shell: bash
+        run: |
+          sudo apt install qemu-user-static
 
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v2
-
-      - name: Login to Quay.io
-        uses: docker/login-action@v2
+      - name: Build container image
+        uses: redhat-actions/buildah-build@v2
         with:
-          registry: quay.io
-          username: 'toolbx-images+github'
-          password: ${{ secrets.QUAY_ROBOT_TOKEN }}
+          platforms: linux/amd64, linux/arm64
+          context: ${{ env.distro }}/${{ matrix.release }}
+          image: ${{ env.distro }}-toolbox
+          tags: ${{ matrix.release }}
+          containerfiles: ${{ env.distro }}/${{ matrix.release }}/Containerfile
+          layers: false
+          oci: true
 
-      - name: Build and push ${{ env.distro_pretty }} ${{ matrix.release }} toolbox image
-        uses: docker/build-push-action@v3
+      - name: Push to Container Registry
+        uses: redhat-actions/push-to-registry@v2
+        id: push
+        if: (github.event_name == 'push' || github.event_name == 'schedule') && github.ref == 'refs/heads/main'
         with:
-          context: ${{ env.distro }}/${{ matrix.release }}
-          file: ${{ env.distro }}/${{ matrix.release }}/Containerfile
-          platforms: linux/amd64,linux/arm64
-          push: true
-          no-cache: true
-          tags: quay.io/toolbx-images/${{ env.distro }}-toolbox:${{ matrix.release }}
+          username: ${{ secrets.BOT_USERNAME }}
+          password: ${{ secrets.BOT_SECRET }}
+          image: ${{ env.distro }}-toolbox
+          registry: ${{ env.REGISTRY }}
+          tags: ${{ matrix.release }}
 
       - name: Push latest tag
-        if: env.latest_release == matrix.release
-        uses: docker/build-push-action@v3
+        uses: redhat-actions/push-to-registry@v2
+        if: (github.event_name == 'push' || github.event_name == 'schedule') && github.ref == 'refs/heads/main' && env.latest_release == matrix.release
         with:
-          context: ${{ env.distro }}/${{ matrix.release }}
-          file: ${{ env.distro }}/${{ matrix.release }}/Containerfile
-          platforms: linux/amd64,linux/arm64
-          push: true
-          tags: quay.io/toolbx-images/${{ env.distro }}-toolbox:latest
+          username: ${{ secrets.BOT_USERNAME }}
+          password: ${{ secrets.BOT_SECRET }}
+          image: ${{ env.distro }}-toolbox
+          registry: ${{ env.REGISTRY }}
+          tags: latest