Kernel: Add a CLI service

* Allows registering command line switches and their handlers from
  plugin activators (start method).
* The handler execution must be executed after ALL other services were
  started. For instance, this can be done from the RCP.
* Handlers support consuming a switch and an additional argument.

Issue-Ref: 3993
Issue-Url: https://af3-developer.fortiss.org/issues/3993


Signed-off-by: Alexander Diewald <diewald@fortiss.org>