declare explicit support for room filtering (MSC3827)

conduit has supported this for a while now and is a Matrix 1.4 feature

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

src/api/client_server/unversioned.rs

@@ -37,6 +37,7 @@ pub async fn get_supported_versions_route(
         unstable_features: BTreeMap::from_iter([
             ("org.matrix.e2e_cross_signing".to_owned(), true),
             ("org.matrix.msc2836".to_owned(), true),
+            ("org.matrix.msc3827".to_owned(), true),
             ("org.matrix.msc2946".to_owned(), true),
         ]),
     };