Default X-Client-Info header

[awalias]

we're rolling out a header similar to Stripe's App-Data in all of the client libs so issues can be debugged more easily between the client and the backend

the javascript libs are done already: supabase/supabase-js#238

the format is: X-Client-Info: supabase-js/1.11.0

for client libs that wrap others (like how supabase-js wraps gotrue-js) we allow the wrapper lib to overwrite the wrapped lib's header (given that we can infer the gotrue-js version based on which supabase-js was used to make the call)

any help with rolling this out here would be incredible

[lqmanh]

With the latest commit, Postgrest-py now allows setting custom headers in PostgrestClient's constructor. The rest should be handled by Supabase-py. I'll open a PR in a few days if I have free time.