Add automation to support building and pushing image to Docker Hub au…

…tomatically (#27)

* Add automation to support building and pushing image

* Remove default shell

The shell is set to bash by default. We don't need to explicitely set it

* Add comment explaining the push criteria for docker

.github/workflows/package.yml

@@ -0,0 +1,40 @@
+name: Build and publish
+
+on:
+  pull_request: {}
+  push:
+    branches:
+      - master
+    tags:
+      - '[0-9]+.[0-9]+.[0-9]+'
+
+jobs:
+  build-docker:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      - name: Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ github.repository_owner }}/duplicity
+          tags: |
+            type=ref,event=branch
+            type=ref,event=pr
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+      - name: Build docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: latest/
+          file: ./latest/Dockerfile
+          # Pushing only when we are running the workflow from a tag
+          # See https://docs.github.com/en/actions/learn-github-actions/contexts#github-context
+          push: ${{ startsWith(github.ref, 'refs/tags') }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}