Rename supabase package to supabase-dart

[Vinzent03]

Rename supabase package to supabase-dart. With all the warnings on readme, and docs, there are still people using the supabase package on a Flutter project and complaining something isn't working.

Originally posted by @dshukertjr in #790

[spydon]

Just a note, since there isn't a rename feature in pub.dev (to not break builds), we would have to create a new package on pub.dev and deprecate the old one with a reference link (built-in functionality in pub.dev) to the new one.