Copy slack notification job from CBL

The CI process for Find doesn't currently post a Slack message if a
deploy fails, like we do in other services.

To implement this, begin by copying over the job definition from
Children's barred list. This will need modifying to work with Find's
particular Azure keyvault structure before it will function correctly.

.github/workflows/build-and-deploy.yml

@@ -75,6 +75,7 @@ jobs:
       url: ${{ steps.deploy.outputs.environment_url }}
     outputs:
       environment_url: ${{ steps.deploy.outputs.environment_url }}
+      environment_name: ${{ matrix.environment }}
 
     steps:
       - uses: actions/checkout@v4
@@ -103,6 +104,7 @@ jobs:
 
     outputs:
       environment_url: ${{ steps.deploy.outputs.environment_url }}
+      environment_name: 'production'
 
     steps:
       - uses: actions/checkout@v4
@@ -113,3 +115,58 @@ jobs:
           docker_image: ${{ needs.docker.outputs.docker_image }}
           azure-credentials: ${{ secrets.AZURE_CREDENTIALS }}
           arm-access-key: ${{ secrets.ARM_ACCESS_KEY }}
+
+  notify_slack_of_failures:
+    name: Notify Slack of failures
+    runs-on: ubuntu-latest
+    needs:
+      [docker, deploy_nonprod, deploy_production]
+    environment: ${{ needs.deploy_production.outputs.environment_name || needs.deploy_nonprod.outputs.environment_name || 'unknown'}}
+    env:
+      ENVIRONMENT_NAME: ${{ needs.deploy_production.outputs.environment_name || needs.deploy_nonprod.outputs.environment_name }}
+    if: failure()
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set Environment variables
+        shell: bash
+        working-directory: terraform
+        run: |
+          if ${{ needs.docker.result == 'failure' }}
+          then
+            job=docker
+          elif ${{ needs.deploy_nonprod.result == 'failure' }}
+          then
+            job=deploy_nonprod
+          elif ${{ needs.deploy_production.result == 'failure' }}
+          then
+            job=deploy_production
+          fi
+          tf_vars_file=aks/config/${{ env.ENVIRONMENT_NAME }}.tfvars.json
+          echo "KEY_VAULT_NAME=$(jq -r '.key_vault_name' ${tf_vars_file})" >> $GITHUB_ENV
+          echo "KEY_VAULT_INFRA_SECRET_NAME=$(jq -r '.key_vault_infra_secret_name' ${tf_vars_file})" >> $GITHUB_ENV
+          echo "JOB=${job}" >> $GITHUB_ENV
+          echo "REVIEW=${review}" >> $GITHUB_ENV
+
+      - uses: Azure/login@v1
+        with:
+          creds: ${{ secrets.AZURE_CREDENTIALS }}
+
+      - uses: DfE-Digital/keyvault-yaml-secret@v1
+        id: get_monitoring_secret
+        with:
+          keyvault: ${{ env.KEY_VAULT_NAME }}
+          secret: ${{ env.KEY_VAULT_INFRA_SECRET_NAME }}
+          key: SLACK_WEBHOOK
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Notify Slack channel on job failure
+        uses: rtCamp/action-slack-notify@v2
+        env:
+          SLACK_USERNAME: CI Deployment
+          SLACK_TITLE: Deployment of check-the-childrens-barred-list ${{ env.REVIEW && 'review' }} failed
+          SLACK_MESSAGE: Job ${{ env.JOB }} failed
+          SLACK_WEBHOOK: ${{ steps.get_monitoring_secret.outputs.SLACK_WEBHOOK }}
+          SLACK_COLOR: failure
+          SLACK_FOOTER: Sent from Build and Deploy workflow