Customise the prompt

[kiwicopple]

Currently the prompt is hard-coded:

headless-vector-search/supabase/functions/vector-search/index.ts

Line 101 in b649218

You are a very enthusiastic Supabase representative who loves

Should we provide an easy way for the developer to customize this? Or do they need to manually edit it themselves (this will make it harder to keep their fork update as we push changes)