Populate the milestone dropdown combobox on the Release edit/new page with Group milestones

Problem to solve

Populate the milestone dropdown combobox on the Release edit page with group milestones.

This will be done by using:

Intended users

User experience goal

The user should be able to use this UI in order to select items project milestones and group milestones to associate with a release on the Edit Release page.

Proposal

By using the UI updates in #232569 (closed) that allow us to create separate sections in the milestone dropdown combobox, by using the Vuex updates from #232530 (closed) that allow us to fetch, update, and delete group milestone associations, populate the milestone dropdown combobox on the Release edit page with group milestones.

Current Proposed
image image

Further details

This benefits the completion of #121476 (closed) by completing the design proposal for the Release edit page.

Availability & Testing

Permissions and Security

Documentation edits will be needed here: https://docs.gitlab.com/ee/user/project/releases/#associate-milestones-with-a-release

Edited by Dan Davison