Add Capability for User to Set Default Model

[adu103]

Add the capability for a user to set which Model they'd like to be their default when opening a chat. Right now, if I choose the 3rd model in a list, then go to my Workspace, and back to chat - it reverts. Would be nice to keep this as a User setting so it maintains until changed.

[paullizer]

This feature has been added and is part of the upcoming 0.215.x release