MP Config: Ability to specify root config source directory

At the moment we can specify MP Config config sources as follows:

/subsystem=microprofile-config-smallrye/config-source=reactive-messaging-properties:add(dir=\{path=/etc/config/reactive-messaging-properties})
/subsystem=microprofile-config-smallrye/config-source=rhosak-binding:add(dir=\{path=/bindings/kafka-config})

The /bindings and /etc/config locations are specific locations under which OpenShift adds service bindings and config map data respectively. The inconvenience of this is that people need to know the exact name of the service bindings/config maps they want to add.

It would be nice to be able to specify root directories as follows, which would then automatically add all the config sources found in the sub-directories. So rather than above, the following would add the same directories as in the above example, as well as all the sibling directories:

/subsystem=microprofile-config-smallrye/config-source-root=config-maps:add(dir=\{path=/etc/config})
/subsystem=microprofile-config-smallrye/config-source-root=service-bindings:add(dir=\{path=/bindings})