When we receive a request on the router port, we should enter the service layer via ServiceEntryPointMongos/strategy.cpp when running a mongod in embedded router mode. This ticket covers:

• Tagging Client and OperationContext as needed with information as to what role the client/operation is acting under
• Code changes in ServiceEntryPointImpl/ServiceStateMachine so that router-requests on mongod (when running in embedded router mode) are dispatched via ServiceEntryPointMongos::handleRequest
• If needed, updating ServiceEntryPoint implementations to use the correct command registry, so ServiceEntryPointMongos uses the router-role command registry and ServiceEntryPointComman uses the shard-role command registry