Mark owner on DriverSessionOptions as optional

I’m running into the issue that owner is not marked as optional in ClientSessionOptions, even though the user would not be expected to provide that option directly to startSession.

NOTE: if this cannot be marked as optional, please let me know what the shell needs to send for this option when calling startSession. We can store a Symbol.for('@@mongosh.shellSession') locally and pass it each time we start a session?