Create backend route for dedicated Release page

What does this MR do?

Creates a backend route and Haml page for the dedicated Release page that will be implemented as part of #32827 (closed).

Feature flag

These changes are hidden behind a release_show_page feature flag, which is disabled by default.

Screenshots

When the release_show_page is enabled:

(Empty page is expected at this point in time 🙂)

Dependencies

This MR includes a cherry-picked commit (67bdf7b0) that is being separately reviewed and merged in !23810 (merged).