MPCONFIG: identify non-static settings

As part of the community call on 2021-02-23, @scolapasta mentioned that historically the database settings had been introduced to make config changes during runtime easier without restarting the deployment/application server. Notes for the talk, Slides of the talk, Recording of the talk

Before migrating all JVM options and Database settings to be configurable via MicroProfile Config, we should identify which settings are crucial to be updated without a restart.

Please note: this does not hold us back from still using MicroProfile Config for those. We just have to make extra sure and double check that the code re-reads any updated setting instead of injecting it statically (either by accessing it programmatically or going for injecting via Provider<>). We should also add a statement to the docs about this fact and which sources not to use then.

So, looking at you @donsizemore, @pdurbin, @landreev, @scolapasta and so many others with experience in running the service: please feel free to add your favorite dynamic setting/s below. I will edit this first comment with an updated list for each.

If there is a JVM option that hasn't been dynamic before, but you feel it should BECOME dynamic, please also comment below.

Thank you folks!