Add workflow to build and push powa-archivist-git

This is done for each commit on this repository.  But since the real source
lives in the powa-archivist repository, it also listen to a repository dispatch
event named "powa-archivist-git", so that we can evnetually trigger a build for
each commit on the source repository.

.github/workflows/powa-archivist_git.yml

@@ -0,0 +1,56 @@
+name: Publish powa-archivist-git container images
+
+# Runs on a new commit on the master branch or when receivind a repopsitory
+# dispatch event by the name of "powa-archivist-git".
+on:
+  push:
+    branches: [master]
+  repository_dispatch:
+    types: [powa-archivist-git]
+
+env:
+  ORG: "powateam"
+  IMAGE_NAME: "powa-archivist-git"
+  REGISTRY: "index.docker.io"
+
+jobs:
+  build_and_push:
+    name: Build powa-archivist-git container images and push to Docker hub
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+      contents: read
+      attestations: write
+      id-token: write
+    steps:
+      - name: Check out the repo
+        uses: actions/checkout@v4
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@0d4c9c5ea7693da7b068278f7b52bda2a190a446
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@8e5442c4ef9f78752691e2d8f8d19755c6f78e81
+        with:
+          images: ${{ env.ORG }}/${{ env.IMAGE_NAME }}
+
+      - name: Build and push images
+        id: push
+        uses: docker/build-push-action@ca052bb54ab0790a636c9b5f226502c73d547a25
+        with:
+          context: ./powa-archivist-git
+          file: ./powa-archivist-git/Containerfile
+          push: true
+          tags: ${{ env.ORG }}/${{ env.IMAGE_NAME}}:latest
+          labels: ${{ steps.meta.outputs.labels }}
+
+      - name: Generate artifact attestation
+        uses: actions/attest-build-provenance@v1
+        with:
+          subject-name: ${{ env.REGISTRY }}/${{ env.ORG }}/${{ env.IMAGE_NAME}}
+          subject-digest: ${{ steps.push.outputs.digest }}
+          push-to-registry: true