implement unstable MSC2666 support for querying mutual rooms

https://github.com/matrix-org/matrix-spec-proposals/pull/2666

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

src/api/client_server/mod.rs

@@ -29,6 +29,7 @@ mod thirdparty;
 mod threads;
 mod to_device;
 mod typing;
+mod unstable;
 mod unversioned;
 mod user_directory;
 mod voip;
@@ -64,6 +65,7 @@ pub use thirdparty::*;
 pub use threads::*;
 pub use to_device::*;
 pub use typing::*;
+pub use unstable::*;
 pub use unversioned::*;
 pub use user_directory::*;
 pub use voip::*;