Allow NetworkManager_dispatcher_t send the SIGKILL signal
to nm-dispatcher plugins which are a part of the
networkmanager_dispatcher_plugin attribute.

The commit addresses the following AVC denial:
type=AVC msg=audit(1718350338.265:319): avc:  denied  { sigkill } for  pid=1790 comm="nm-dispatcher" scontext=system_u:system_r:NetworkManager_dispatcher_t:s0 tcontext=system_u:system_r:NetworkManager_dispatcher_custom_t:s0 tclass=process permissive=0

Resolves: rhbz#2292370