SpringBoot Allow the configprops endpoint to return properties with a particular prefix

Adds ability to filter by prefix for /actuator/configprops

Fixes gh-24714

No filter

Filter by prefix

(ℹ️ this was taken from v1 screenshot and url does not contain prefix param anymore)

Comment From: snicoll

nicely done Chris. I've polished your contribution in b92bb93. The interesting bits is that we name the method differently when there is a selector so that the JMX operation (that uses the method name) can provide a bit more context as what it does compared to the general operation.

Thanks again!