Draft: Migrates Gitlab Pages to Slog and away from logrus

What does this MR do?

This MR migrates the server.go part of pages away from logrus and towards slog which has been determined as the strategic library going forward.

This is testing the waters on a lower-risk part of our system prior to rolling this out more generally across all Go components. I suspect this will not have any meaningful performance improvements.

I've also taken the liberty of moving the maxprocs call to the main function and away from an init function. We should avoid the init function where possible - https://www.bytesizego.com/blog/init-function-golang

TODO

• Feature flag

  • Added feature flag:

  • This feature does not require a feature flag

• I added the Changelog trailer to the commits that need to be included in the changelog (e.g. Changelog: added)
• 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