Expose the agent modes when submitting a prompt

[DonJayamanne]

Currently in CLI its possible to toggle between different modes: autopilot, interactive or plan
Would like the same to be exposed in SDK as well.

I can see that we have something similar for fleet, though thats more of a command
Perhaps we can have the autopilot, interactive and plan exposed as commands or the like.
Not sure

[MackinnonBuck]

This is currently supported via session.rpc.mode.set(params: ModeSetRequest) and session.rpc.mode.get().