feat: make _redirects limits configurable

What does this MR do?

This makes the hardcoded limits in _redirects configurable per instance, so self-managed pages can configure and benchmark their own, without relying on issues like Optimize redirect system and find appropriate m... (#472 - closed).

Companion MRs depending on this one:

• Omnibus feat: make pages _redirects limits configurable (omnibus-gitlab!6144 - merged)
• GitLab docs Add documentation for configurable _redirects l... (gitlab!89780 - merged)

TODO

• I added the Changelog trailer (e.g. Changelog: added) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines

🛠 with ❤ at Siemens