misc-progs: addonctrl: Add support for 'Services' metadata

misc-progs: addonctrl: Add support for 'Services' metadata

* Addonctrl will now check in addon metadata for the exact initscript
  names (Services). If more than one initscript is defined for an addon,
  the requested action will be performed on all listed initscripts.
* Added posibility to perform action on a specific initscript of an
  addon instead of on all initscripts of the addon.
* New action 'list-services' to display a list of services related to
  an addon.
* New action 'boot-status' to display wether service(s) are enabled
  to start on boot or not.
* More error checking and cleaner error reporting to user
* General cleanup and code restructuring to avoid code duplication
* Updated and made usage instructions more verbose.

Fixes: Bug#12935
Signed-off-by: Robin Roevens <robin.roevens@disroot.org>
Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>