Update cloud-platform-maintenance-page docker-build workflow file

[timckt]

Background

In cloud-platform-maintenance-page, the github workflow is using pushing image to DockerHub rather than ECR.

It is not updated and not align with the Readme file which mentions Configure the Github actions to build the maintenance page image to your ECR.

jobs:
  docker:
    name: Build container and push to DockerHub
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v3

      - name: Set up QEMU
        uses: docker/setup-qemu-action@v2

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v2

      - name: Login to DockerHub
        uses: docker/login-action@v1
        with:
          username: ${{ secrets.DOCKER_USERNAME }}
          password: ${{ secrets.DOCKER_PASSWORD }}

      - name: Get Tags for Image
        id: metadata
        uses: docker/metadata-action@v4
        with:
          images: ministryofjustice/cloud-platform-maintenance-page
          tags: |
            type=ref,event=tag

      - name: Build and push
        uses: docker/build-push-action@v3
        with:
          context: .
          push: true
          tags: ${{ steps.metadata.outputs.tags }}

Update it to be ECR focused and align with the Readme instruction.

Workflow reference here for pushing to ECR

Proposed user journey

Approach

Which part of the user docs does this impact

Communicate changes

• [ ] post for #cloud-platform-update
• [ ] Weeknotes item
• [ ] Show the Thing/P&A All Hands/User CoP
• [ ] Announcements channel

Questions / Assumptions

Definition of done

• [ ] readme has been updated
• [ ] user docs have been updated
• [ ] another team member has reviewed
• [ ] smoke tests are green
• [ ] prepare demo for the team

Reference

How to write good user stories