add support for serving client+server well-known and /client/server.json endpoints from conduwuit

the last endpoint is a non-standard health check endpoint used by at
least Element Web as a weird way to determine if syncv3 is available

there can also be some valid use-cases for serving well-knowns from the
application itself

Signed-off-by: strawberry <strawberry@puppygock.gay>

src/config/mod.rs

@@ -70,6 +70,7 @@ pub struct Config {
     #[serde(default = "default_default_room_version")]
     pub default_room_version: RoomVersionId,
     pub well_known_client: Option<String>,
+    pub well_known_server: Option<String>,
     #[serde(default)]
     pub allow_jaeger: bool,
     #[serde(default)]