Allow configuring the default click action for Chat Sessions

Add a setting that controls whether clicking a Chat Session opens it in the Chat sidebar or as an editor, with the modifier-click action performing the alternative behavior.

Personally, I like the secondary side bar to just be a list of chats with open chats in the editor area. I don't ever want to open a chat in the secondary side bar. Currently, I have to use the modifier key every time I click on a chat that's not currently open in the editor area.