feat: Stabilize Session Config Options

[benbrandt]

Proposing to move this to the Completed stage!

[chazcb]

@benbrandt would love if you took a quick look at #393 and the different config schema there. It might make sense to consolidate the way we define config schemas together.

[benbrandt]

@chazcb a few thoughts:

• First: sorry for not doing a full review on that one sooner
• Second: we made session config options possible to add new variants in the future, so I don't think it is at odds
• Third: Session config options has something yours doesn't yet, which is the ability to have a distinction between values and labels, i.e. a unique ID and a user-facing value, but we can address that on your RFD

[benbrandt]

OK going to stabilize this!