The /_matrix/client/unstable/org.matrix.simplified_msc3575/sync endpoint
can be handled by generic workers, but Synapse's workers.md documentation
doesn't mention it. The code confirms it's worker-compatible:

- SlidingSyncRestServlet is registered via sync.register_servlets:
  https://github.com/element-hq/synapse/blob/0dfcffab0f/synapse/rest/client/sync.py#L1128-L1131

- sync.register_servlets is NOT in the worker exclusion list:
  https://github.com/element-hq/synapse/blob/0dfcffab0f/synapse/rest/__init__.py#L180-L194

- GenericWorkerStore includes SlidingSyncStore:
  https://github.com/element-hq/synapse/blob/0dfcffab0f/synapse/app/generic_worker.py#L168

This adds the endpoint to both:
- matrix_synapse_workers_sync_worker_client_server_endpoints (for specialized sync workers with sticky routing)
- matrix_synapse_workers_generic_worker_endpoints (documenting generic worker capability)