Implement /thirdparty endpoints

[S7evinK]

Implements the following endpoints

GET /_matrix/client/v3/thirdparty/protocols
GET /_matrix/client/v3/thirdparty/protocols/{protocol}
GET /_matrix/client/v3/thirdparty/location
GET /_matrix/client/v3/thirdparty/location/{protocol}
GET /_matrix/client/v3/thirdparty/user
GET /_matrix/client/v3/thirdparty/user/{protocol}

[neilalexander]

Looks like there are newly passing tests for sytest-whitelist.

[S7evinK]

Yep, but I'm not yet happy with the cache, as it is only refreshed when calling /protocol without a protocol.

[S7evinK]

Oh, and this would need matrix-org/sytest#1310, which currently breaks the tests for Synapse.
Even with the fallback implemented, the tests fail due to Destroying unresponded HTTP request to /appservs/1/_matrix/app/v1/thirdparty/protocol/ymca