Make it possible to create a Release through the UI

Problem to solve

It is only possible to create a Release using the Releases API.

Proposal

In #26016 (closed), we added the ability to edit a release using the UI. We should reuse this UI to create a new Release.

Further details

Creating a Release was included in the original scope of #26016 (closed), but this feature was trimmed in an effort to deliver value incrementally.

Creating a Release is slightly more complicated than editing a Release, because we will need the ability to select a Git tag. The current "Edit Release" page does not allow the tag to be changed, so it doesn't already have a tag selector built-in.

Documentation

This page will need to be updated with instructions on using the UI to create a Release.