Add initial MSC4186 (Simplified Sliding Sync) implementation

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

src/api/client/unversioned.rs

@@ -52,6 +52,7 @@ pub(crate) async fn get_supported_versions_route(
 			("org.matrix.msc4180".to_owned(), true), /* stable flag for 3916 (https://github.com/matrix-org/matrix-spec-proposals/pull/4180) */
 			("uk.tcpip.msc4133".to_owned(), true), /* Extending User Profile API with Key:Value Pairs (https://github.com/matrix-org/matrix-spec-proposals/pull/4133) */
 			("us.cloke.msc4175".to_owned(), true), /* Profile field for user time zone (https://github.com/matrix-org/matrix-spec-proposals/pull/4175) */
+			("org.matrix.simplified_msc3575".to_owned(), true), /* Simplified Sliding sync (https://github.com/matrix-org/matrix-spec-proposals/pull/4186) */
 		]),
 	};