Add prod approval gate after int

[UmeshBangaNHS]

Summary

Adds an explicit manual approval stage between int and prod in the release pipeline.

This prevents the production deployment from starting immediately after the existing non-prod stages and makes the intended release order:

1. internal-dev
2. int
3. prod_approval
4. prod

Validation

• Confirmed the branch diff against origin/master contains only azure/azure-release-pipeline.yml.
• Ran git diff --check origin/master..HEAD -- azure/azure-release-pipeline.yml.
• Parsed azure/azure-release-pipeline.yml with PyYAML from the repo virtualenv.
• Asserted the release deployment graph locally:
  • int depends on internal_dev
  • prod_approval depends on int
  • prod depends on prod_approval
  • the template auto prod approval is disabled with prod_requires_approval: false
• Checked the shared NHSDigital/api-management-utils edge templates support explicit manual-approval deployments and pass through manual_approval_env and depends_on.

Azure still needs to validate the full server-side template expansion on the PR.

[github-actions]

This branch is work on a ticket in the NHS Digital APM JIRA Project. Here's a handy link to the ticket:

APM-000