docs: Document more settings (#36993)

Within our hosted docs, we are missing documentation for quite a lot of
settings - sometimes for newer settings, sometimes for settings that are
more than two years old. This leads (amongst other things) to feature
requests for features that are already supported, false issue reports
(because people couldn't find the setting for what caused the issue
within the documentation) and generally just takes time for for both
these affected by the missing documentation as well as these handling
the questions around it.

This change here takes a stab at the problem by adding more
documentation for a lot supported setting (not all of it) as well as
reorganizing some settings so that some stuff can (hopefully) be found
more easily. Eventually, we should find a better method for this, but
it's still better than informing people for the n-th time that we e.g.
have `agent_font_size` for the agent panel. Manually audited twice but
I'll take another thorough look before merging.

Release Notes:

- N/A

Author: MrSubidubi