Implemented functions and combined with auth fixes from elijahmorg

[roja]

What kind of change does this PR introduce?

This makes the client significantly more useful for people using functions, it includes the improvements made by elijahmorg which improve the experience for users who make use of auth.

Relies on this pull request: https://github.com/supabase-community/functions-go/pull/2 and this: https://github.com/supabase-community/postgrest-go/pull/48