Add workflow for publishing beta

.github/workflows/publish_beta.yaml

@@ -0,0 +1,48 @@
+name: Publish ROCK (beta)
+on:
+  workflow_dispatch:
+    branches:
+      - '[0-9]-[0-9][0-9].[0-9][0-9]'
+
+jobs:
+  build:
+    uses: ./.github/workflows/build.yaml
+  publish:
+    needs: build
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    permissions:
+      packages: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+      - name: Setup Docker
+        run: |
+          sudo snap install docker
+          sudo addgroup --system docker; sudo adduser $USER docker
+          newgrp docker
+          sudo snap disable docker; sudo snap enable docker
+      - name: Install skopeo
+        run: |
+          sudo snap install --devmode --channel edge skopeo
+      - name: Install yq
+        run: |
+          sudo snap install yq
+      - uses: actions/download-artifact@v3
+        with:
+          name: mongodb-rock
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ secrets.GHCR_USER }}
+          password: ${{ secrets.GHCR_TOKEN }}
+      - name: Import and push to GHCR
+        run: |
+          version=$(yq '(.version)' rockcraft.yaml)
+          base=$(yq '(.base|split("@"))[1]' rockcraft.yaml)
+          tag=${version}-${base}_beta
+          sudo skopeo --insecure-policy copy \
+            oci-archive:charmed-mongodb_${version}_amd64.rock \
+            docker-daemon:ghcr.io/canonical/charmed-mongodb:${tag}
+          docker push ghcr.io/canonical/charmed-mongodb:${tag}