ui2: add enforce flag

[JonasBa]

Add a flag to opt users into UI2 and the new experience

[natemoo-re]

In favor of this! Should we consider exposing a hook for this or do we want to replicate the check where we need it?

[JonasBa]

In favor of this! Should we consider exposing a hook for this or do we want to replicate the check where we need it?

It seems like an overkill to me tbh, we only need this in two places, and it'll all get removed once we are GA