MPCONFIG: move JvmSettings to SPI (was: allow to retrieve all values used for a placeholder scoped setting)

[poikilotherm]

Overview of the Feature Request
We need to move the JVM settings stuff into the SPI package, so people writing exporters and other modular stuff can reuse the configuration lookup things in their modules.

~~For JVM options that contain placeholders, we usually provide the substitution value in some way to lookup the configuration value.

It is currently not possible to retrieve a list of used values for a placeholder, determined from settings provided by a sysadmin.~~

It might no longer be necessary to add this, as we seem to come to a consensus that it's OK to have a list of things to look for. See the new PID settings.

What kind of user is the feature intended for?
Sysadmin

What inspired the request?
This is currently necessary for storage configuration (#9998), but is likely to be used in the future, when we enable multiple instances of PID providers (#3623). No longer true. One of the inspirations to move these things is now #10048

What existing behavior do you want changed?
See above.

Any brand new behavior do you want to add to Dataverse?
Nope

Any open or closed issues related to this feature request?
#7000 #3623 #9998