Compliance frameworks: post migration workflow

What does this MR do and why?

How to validate locally

1. Enable feature flag ff_compliance_pipeline_maintenance_mode in rails console (rails c): Feature.enable :ff_compliance_pipeline_maintenance_mode
2. Visit compliance center Docs
3. Create a framework which uses pipeline configuration path
4. Save framework, enter editing of this framework
5. Observe deprecation warning
6. Click 'Migrate pipeline to a policy'
7. Observe prefilled form
8. Create merge request
9. Observer merge request title and description
10. Merge this merge request and go back to compliance framework editing page
11. Observe that deprecation warning changed text

MR acceptance checklist

Please evaluate this MR against the [MR acceptance checklist] (https://docs.gitlab.com/ee/development/code_review.html#acceptance-checklist). It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Related to #476626 (closed)