Tasks to deprecate Migrate Drupal UI

Problem/Motivation

Track the steps needed to deprecate extension Migrate Drupal UI. See Remove a core module and move it to a contributed project of the deprecation policy.

The removal of extension Migrate Drupal UI was approved in #3371229: [Policy] Migrate Drupal and Migrate Drupal UI after Drupal 7 EOL. It is happen after Drupal 7 is EOL.

Remaining tasks

1. Do a thorough search of core for any remaining references to the extension. If references are found, outside of the extension, then create issues to remove the references.
2. Create a section on Deprecated and obsolete modules and themes to provide recommendations for sites using extension EXTENSION_NAME. The recommendations are to include instructions for sites using the extension and for contributed projects that depend on then extension.
3. Add the following to the extension info.yml file

lifecycle: deprecated
lifecycle_link: https://www.drupal.org/node/3223395#s-EXTENSION

4. Add @group legacy to all tests in the extension.
5. Add a change record and include a link the the doc page.
6. Deprecate any library that is only used by the extension.

Release notes snippet