Add links to associated release(s) to the milestone detail page sidebar

What does this MR do?

Adds links to the associated release(s) to the milestone detail page as described in #29020 (closed):

These links only appear if the milestone is a project milestone. Group milestones cannot be associated with a release (since releases are directly tied to a git tag), so this section is not rendered for group milestones.

Screenshots

No associated release:

Sidebar expanded:

Sidebar collapsed:

One associated release:

Sidebar expanded:

Sidebar collapsed:

Multiple associated releases:

Sidebar expanded:

Sidebar collapsed: