feat(telescope): telescope flat style support

[nottyl]

Updates the Telescope integration to allow users to choose a telescope style between "nvchad" and "classic".
The default style currently is set to "classic"

• Classic (the original style):

• Nvchad (flat style)

[nullchilly]

Please keep backwards compatibility, O.integrations.telescope was a boolean before and can't be indexed

The default should be classic since we respect plugin's theme guideline

I think we should rename flat -> nvchad since it's the original

[nottyl]

Ok! I changed the name flat to nvchad and included backward compatibility in the latest commit. Though I don't know how to implement backward compatibility correctly so the code might be a bit ugly :<

[mrtnvgr]

LGTM! Thanks!