coredump: support tracing of secured cores via polkit

this touches a huge chunk of technology. the previous invocation through coredumpctl debug has been removed entirely. instead we now always prepare the debugger by extracting the core using coredumpctl dump, depending on whether the actual core file is readable by drkonqi directly that happens in-process, or via the polkit helper.

the polkit helper essentially does the same thing but in root scope.

since debugger preparation has no retry system in place we don't really have a way to deal with the user denying authorization. we simply pretend all went well. internally we then mark sentry for skipping so it looks like all is grand, but in reality it isn't. there isn't anything the user can do about this anyway once authorization was denied.