fix: allow configure json library for supabase libs

[zoedsoupe]

Problem

Some libraries from the elixir-supabase ecosystem are using JSON (native elixir module introduced on 1.18) and others are using Jason for JSON encoding, this creates a version mismatch for elixir version requirement since the supabase-ex supports from 1.16 to 1.18, so the rest of the libraries should do the same

Solution

For that to work, i've introduced the json_library app config for supabase, similar to what Phoenix does, defaulting to Jason since historically is the most used JSON encoding library in elixir.

Rationale

N/A

[zoedsoupe]

after launching a new release of this library, and after #68 i will update all other dependencies to use this function instead of json modules directly, so we can enforce the ~> 1.16 elixir version support for all the libraries consistently