Handle /notifications endpoint via workers

Related to https://github.com/matrix-org/synapse/pull/16265

roles/custom/matrix-synapse/vars/main.yml

@@ -170,6 +170,7 @@ matrix_synapse_workers_generic_worker_endpoints:
   - ^/_matrix/client/(r0|v3|unstable)/user/.*/filter(/|$)
   - ^/_matrix/client/(api/v1|r0|v3|unstable)/directory/room/.*$
   - ^/_matrix/client/(r0|v3|unstable)/capabilities$
+  - ^/_matrix/client/(r0|v3|unstable)/notifications$
 
   # Encryption requests
   # Note that ^/_matrix/client/(r0|v3|unstable)/keys/upload/ requires `worker_main_http_uri`