Deploy github workflow

These workflow setups seem pretty much identical across projects. So, as
standard, this:
1. builds the container image
2. pushes it to ECR
3. updates the image tag in govuk-helm-charts

The cronjob (that we're planning to add to govuk-helm-charts) will then
pull the released image the next time it runs.

Until we're ready to put this into production, we'll test this by
deploying to integration. After that, we might choose to still keep
integration available for testing. (But note the promotion from one
environment to the next won't be needed for this project.)

.github/workflows/deploy.yml

@@ -0,0 +1,44 @@
+name: Deploy
+
+run-name: Deploy ${{ inputs.gitRef || github.ref_name  }} to ${{ inputs.environment || 'integration' }}
+
+on:
+  workflow_dispatch:
+    inputs:
+      gitRef:
+        description: 'Commit, tag or branch name to deploy'
+        required: true
+        type: string
+      environment:
+        description: 'Environment to deploy to'
+        required: true
+        type: choice
+        options:
+        - integration
+        - staging
+        - production
+        default: 'integration'
+  release:
+    types: [released]
+
+jobs:
+  build-and-publish-image:
+    if: github.event_name == 'workflow_dispatch' || startsWith(github.ref_name, 'v')
+    name: Build and publish image
+    uses: alphagov/govuk-infrastructure/.github/workflows/build-and-push-image.yml@main
+    with:
+      gitRef: ${{ inputs.gitRef || github.ref_name }}
+    secrets:
+      AWS_ACCESS_KEY_ID: ${{ secrets.AWS_GOVUK_ECR_ACCESS_KEY_ID }}
+      AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_GOVUK_ECR_SECRET_ACCESS_KEY }}
+  trigger-deploy:
+    name: Trigger deploy to ${{ inputs.environment || 'integration' }}
+    needs: build-and-publish-image
+    uses: alphagov/govuk-infrastructure/.github/workflows/deploy.yml@main
+    with:
+      imageTag: ${{ needs.build-and-publish-image.outputs.imageTag }}
+      environment: ${{ inputs.environment || 'integration' }}
+    secrets:
+      WEBHOOK_TOKEN: ${{ secrets.GOVUK_ARGO_EVENTS_WEBHOOK_TOKEN }}
+      WEBHOOK_URL: ${{ secrets.GOVUK_ARGO_EVENTS_WEBHOOK_URL }}
+      GH_TOKEN: ${{ secrets.GOVUK_CI_GITHUB_API_TOKEN }}