ci: add manual docker image release (#7597)

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

+# Trigger this workflow only to manually create a Docker release; this should only be used
+# in extraordinary circumstances, as Docker releases are normally created automatically as
+# part of the automated release workflow.
+
+name: release-manual-docker
+on:
+  workflow_dispatch:
+    inputs:
+      ref:
+        default: ''
+        description: 'Reference (tag / SHA):'  
+env:
+  REGISTRY: docker.io
+  IMAGE_NAME: parseplatform/parse-server
+jobs:
+  build:
+    runs-on: ubuntu-18.04
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Determine branch name
+        id: branch
+        run: echo "::set-output name=branch_name::${GITHUB_REF#refs/*/}"
+      - name: Checkout repository
+        uses: actions/checkout@v2
+        with:
+          ref: ${{ github.event.inputs.ref }}
+      - name: Set up QEMU
+        id: qemu
+        uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Log into Docker Hub
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      - name: Extract Docker metadata
+        id: meta
+        uses: docker/metadata-action@v3
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          flavor: |
+            latest=${{ steps.branch.outputs.branch_name == 'master' && github.event.inputs.ref == '' }}
+          tags: |
+            type=semver,enable=true,pattern={{version}},value=${{ github.event.inputs.ref }}
+            type=raw,enable=${{ github.event.inputs.ref == '' }},value=latest
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          platforms: linux/amd64, linux/arm/v6, linux/arm/v7, linux/arm64/v8
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}