Do not send client metadata on regular operation.IsMaster.Execute invocations

The operaiton.IsMaster type supports two different modes of execution: Execute and Handshake. The Handshake method is called when setting up a new connection and should send client metadata. The Execute method is called during heartbeats and should not send client metadata. To fix this, create a second command method that is used during Execute that does not add client metadata to the document.