ci(docker): add pre-release workflow

This commit adds a pre-release workflow that will push images to Docker Hub with tags based on the pull request head ref.

This will allow us to easily test and deploy pre-release versions of the config editor.

.github/workflows/pre-release-docker.yml

@@ -0,0 +1,34 @@
+name: Pre-Release on Docker Hub
+
+on:
+  push:
+    branches-ignore:
+      - 'main'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+      - name: Login to Docker Hub
+        uses: docker/login-action@v2
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      - name: Build and push
+        uses: docker/build-push-action@v3
+        with:
+          push: true
+          platforms: linux/amd64, linux/arm64
+          tags: communityfirst/mapeo-config-editor:${{ github.event.pull_request.head.ref }}
+      - name: Docker Hub Description
+        uses: peter-evans/dockerhub-description@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+          repository: communityfirst/mapeo-config-editor