This PR adds a homeserver config option, `user_directory.prefer_local_users`, that when enabled will show local users higher in user directory search results than remote users. This option is off by default.
Note that turning this on doesn't necessarily mean that remote users will always be put below local users, but they should be assuming all other ranking factors (search query match, profile information present etc) are identical.
This is useful for, say, University networks that are openly federating, but want to prioritise local students and staff in the user directory over other random users.
The general idea here is that config examples should just have a hash and no
extraneous whitespace, both to make it easier for people who don't understand
yaml, and to make the examples stand out from the comments.
Initial commit; this doesn't work yet - the LIKE filtering seems too aggressive.
It also needs _do_initial_spam to be aware of prepopulating the whole user_directory_search table with all users...
...and it needs a handle_user_signup() or something to be added so that new signups get incrementally added to the table too.
Committing it here as a WIP
Andrew Morgan