Add MSC3030 experimental client and federation API endpoints to get the closest event to a given timestamp (#9445)

MSC3030: https://github.com/matrix-org/matrix-doc/pull/3030

Client API endpoint. This will also go and fetch from the federation API endpoint if unable to find an event locally or we found an extremity with possibly a closer event we don't know about.
```
GET /_matrix/client/unstable/org.matrix.msc3030/rooms/<roomID>/timestamp_to_event?ts=<timestamp>&dir=<direction>
{
    "event_id": ...
    "origin_server_ts": ...
}
```

Federation API endpoint:
```
GET /_matrix/federation/unstable/org.matrix.msc3030/timestamp_to_event/<roomID>?ts=<timestamp>&dir=<direction>
{
    "event_id": ...
    "origin_server_ts": ...
}
```

Co-authored-by: Erik Johnston <erik@matrix.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/synapse/server.py b/synapse/server.py
index 877eba6c08..185e40e4da 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -97,6 +97,7 @@ from synapse.handlers.room import (
     RoomContextHandler,
     RoomCreationHandler,
     RoomShutdownHandler,
+    TimestampLookupHandler,
 )
 from synapse.handlers.room_batch import RoomBatchHandler
 from synapse.handlers.room_list import RoomListHandler
@@ -729,6 +730,10 @@ class HomeServer(metaclass=abc.ABCMeta):
         return RoomContextHandler(self)
 
     @cache_in_self
+    def get_timestamp_lookup_handler(self) -> TimestampLookupHandler:
+        return TimestampLookupHandler(self)
+
+    @cache_in_self
     def get_registration_handler(self) -> RegistrationHandler:
         return RegistrationHandler(self)