Add back warning when clj-kondo extension is detected

[bpringe]

I think that warning is better off staying in Calva...

It appears I thought it was a good idea to remove that warning in the past 😅: https://github.com/BetterThanTomorrow/calva/issues/1091. Sorry @jacobemcken! I think we should add that back...

Originally posted by @bpringe in https://github.com/BetterThanTomorrow/calva/issues/1864#issuecomment-1266360275