Improve tagging (#101)

* Improve tagging so that containers are not just latest

* Remove conditions around PR

* Rename job

* Add GHCR prefix

* Switch to official docker metadata action

* Rename and reindent, stupid yaml

* Make it use GHCR rather than DockerHub

* Remove format owner

.github/workflows/docker.yml

@@ -1,40 +1,45 @@
 name: ci
 
 on:
+  pull_request:
   push:
     branches:
       - 'main'
 
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
 jobs:
   docker:
     runs-on: ubuntu-latest
     steps:
-      -
-        name: Checkout
+      - name: Checkout
         uses: actions/checkout@v2
-      -
-        name: Set up QEMU
+      - name: Set up QEMU
         uses: docker/setup-qemu-action@v1
-      -
-        name: Set up Docker Buildx
+      - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v1
-      -
-        name: Login to GitHub Container Registry
+      - name: Login to GitHub Container Registry
         uses: docker/login-action@v1 
         with:
           registry: ghcr.io
           username: ${{ github.repository_owner }}
           password: ${{ secrets.GITHUB_TOKEN }}
-      - id: formatowner
-        uses: ASzc/change-string-case-action@v1
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v3
         with:
-          string: ${{ github.repository_owner }}
-      -
-        name: Build and push
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=ref,event=branch
+            type=ref,event=pr
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+      - name: Build and push
         uses: docker/build-push-action@v2
         with:
           context: .
           platforms: linux/amd64
           push: true
-          tags: |
-            ghcr.io/${{ steps.formatowner.outputs.lowercase }}/juno:latest
+          tags: ${{ steps.meta.outputs.tags }}