Draft: follow up: slowlogs

What does this MR do?

follow up: slowlogs:

• Make SlowRequestThreshold public.
• Make use of NewNullLogger for the loggerFunc.
• Panic incase of type mismatch for timingInfo.

Related: #1132

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