Support rebind connection(session) to original threadgroup

[xiexiaoy]

Sessions of MongoDB are logical, meaning they are allowed to cross connections. However, transactions in EloqDoc are bound to a ThreadGroup that creates them, and connections in EloqDoc are bound to a ThreadGroup when the connection is accepted.

1. Store the original ThreadGroupId in the Session object.
2. Get the current ThreadGroupId from the ServiceStateMachine(connection) object and the original ThreadGroupId from the Session object.
3. Compare the current ThreadGroupId and the original ThreadGroupId.
4. If they are different, reset the ThreadGroupId of ServiceStateMachine and forward continuation to the original ThreadGroup.
5. Rebind is unnecessary if the incoming command is not inside a transaction.