Automated Image Updates (#17)

* Adds initial workflow file for automatically keeping container images up to date.
* TODO: Still requires testing for the cron schedule to ensure that it is working appropriately.

.github/workflows/update-image.yml

@@ -0,0 +1,31 @@
+name: "Update Image"
+on:
+  # TODO: Remove faster schedule and pull_request once testing is completed.
+  schedule: # Schedled workflows only run once merged into main.
+    - cron: "*/5 * * * *" # Faster schedule for testing.
+    #- cron: "0 12 * * *" # Proposed schedule once testing has completed.
+  pull_request: # Here to ensure the workflow runs during testing. Will be removed once testing is completed.
+    types: [opened, reopened, synchronize]
+jobs:
+  rebuild-container:
+    name: "Rebuild Container"
+    runs-on: ubuntu-latest
+    steps:
+      # Checkout the repo.
+      - name: "Checkout"
+        uses: "actions/checkout@v2"
+
+      # Build and push the repo.
+      - name: "Build and Push"
+        uses: docker/build-push-action@v1
+        with:
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+          registry: docker.pkg.github.com
+          repository: ${{ github.repository }}/simple-monerod
+          tags: latest
+          # TODO: Test that a release tag stays assigned to the rebuilt container when release tagged.
+          tag_with_ref: true
+          # TODO: Evaluate if the following are necessary.
+          add_git_labels: true
+          tag_with_sha: true