Add support for setting `skip_thread_containment`

If set to true Pleroma will not filter out posts from the home timeline even if the user can't access the parent posts are not visible to the current user.

Like other options it can be set in PATCH /api/v1/update_credentials and read under pleroma.skip_thread_containment in the User entity

@hj @shpuld could we get this one before 1.0? it doesn't seem to difficult to add and since thread containment is now disabled by default I am pretty sure many people will ask about that after updating to a new release

mentioned in merge request !860 (closed)

I don't think we should add this anymore, all our thread containment stuff was too slow and we have the thread filtering now.

sorry, i mean reply filtering

Right, we have other means to do this now, properly working reply filtering in backend, and we have info about parent availability elsewhere: #874 (closed)

closed