Add "release" filter to issue search

What does this MR do?

Adds a "release" filter to the issue search interface as part of #32632 (closed). This filter allows issues to be filtered like release:v1.2, where 1.2 is the tag the release is based on.

The list of releases shown after selecting the "release" filter (see the second screenshot below) is ordered by "released at" date.

In addition to a tag name, the user can select "All" or "None". This works identically to the current milestone filter:

• All: Show all issues associated to at least one release
• None: Show all issues not associated to at least one release

Feature flag

This feature is hidden behind a new feature flag: :release_search_filter. It is disabled by default.

Screenshots