Adds prompt so agent doesn't randomly rename session

[Mbeaulne]

Closes: https://github.com/Shopify/oasis-frontend/issues/662

I'm not entirely sure this is what was required from this ticket, but here we are!

• When a user starts a session, the agent will decided what to call the session.
• If a user asks to change the session title the agent will
• If the conversation deviates from the original session topic the agent will NOT rename the session