Prevents a SynapseError being raised inside of a IResolutionReceiver and instead opts to just return 0 results. This thus means that we have to lump a failed lookup and a blacklisted lookup together with the same error message, but the substitute should be generic enough to cover both cases.

This commit adds two config options:

* `restrict_public_rooms_to_local_users`

Requires auth to fetch the public rooms directory through the CS API and disables fetching it through the federation API.

* `require_auth_for_profile_requests`

When set to `true`, requires that requests to `/profile` over the CS API are authenticated, and only returns the user's profile if the requester shares a room with the profile's owner, as per MSC1301.

MSC1301 also specifies a behaviour for federation (only returning the profile if the server asking for it shares a room with the profile's owner), but that's currently really non-trivial to do in a not too expensive way. Next step is writing down a MSC that allows a HS to specify which user sent the profile query. In this implementation, Synapse won't send a profile query over federation if it doesn't believe it already shares a room with the profile's owner, though.

Groups have been intentionally omitted from this commit.

Follow-up to #5124

Also added a bunch of checks to make sure everything (both the stuff added on #5124 and this PR) works as intended.

This endpoint isn't much use for its intended purpose if you first need to get
yourself an admin's auth token.

I've restricted it to the `/_synapse/admin` path to make it a bit easier to
lock down for those concerned about exposing this information. I don't imagine
anyone is using it in anger currently.

It doesn't really belong under rest/client/v1 any more.

Rewrite this so that it doesn't hammer the database.

make sure we store the name of the server the keys came from, rather than the
origin server, after doing a fetch-from-perspectives.

This is a bit fiddly due to the keyring doing weird things with logcontexts.

Remove presence list support as per MSC 1819

Hopefully this time we really will fix #4422.

We need to make sure that the cache on
`get_rooms_for_user_with_stream_ordering` is invalidated *before* the
SyncHandler is notified for the new events, and we can now do so reliably via
the `events` stream.

test threepid checking

Collect all the things that make room-versions different to one another into
one place, so that it's easier to define new room versions.

Redo of https://github.com/matrix-org/synapse/pull/4840

Make sure that they are sent correctly over the replication stream.

Fixes: #4898

I don't have a database with the same name as my user, so leaving the database
name unset fails.

While we're at it, clear out some unused stuff in the test setup.