Push complement image to a docker registry

.github/workflows/push_complement_image.yml

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+# This task does not run complement tests, see tests.yaml instead.
+# This task does not build docker images for synapse for use on docker hub, see docker.yaml instead
+
+name: Store complement synapse image in ghcr.io
+on:
+  push:
+    branches: ["master"]
+  schedule: 
+      - '* 5 * * *'
+
+# Only run this action once per pull request/branch; restart if a new commit arrives.
+# C.f. https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#concurrency
+# and https://docs.github.com/en/actions/reference/context-and-expression-syntax-for-github-actions#github-context
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs: 
+  build:
+    name: Build and push complement image
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+       - name: Checkout clean copy of develop (scheduled build)
+         uses: actions/checkout@v3
+         if: 'github.event.type == "schedule"'
+         with:
+           ref: develop
+       - name: Checkout clean copy of master (on-push)
+         uses: actions/checkout@v3
+         if: 'github.event.type != "schedule"'
+         with:
+           ref: master
+       - name: Login to registry
+         uses: docker/login-action@v1
+         with:
+           registry: ghcr.io
+           username: ${{ github.actor }}
+           password: ${{ secrets.GITHUB_TOKEN }}
+       - name: Work out labels for complement image
+         id: meta
+         uses: docker/metadata-action@v1
+         with: 
+           images: ghcr.io/${{ github.repository }}/complement-synapse
+       - name: Build complement image
+         run: scripts-dev/complement.sh --build-only
+       - name: Tag and push generated image
+         run: |
+           for TAG in ${{ steps.meta.outputs.tags }}; do 
+             docker tag complement-synapse:latest $TAG
+             docker push $TAG
+           done

changelog.d/14509.docker

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+Push complement-synapse docker images to ghcr.io repository.