Feature Request: Port storage functions to plpgsql

[purpleKarrot]

Functions like signObjectUrl are currently implemented in typescript and have to be called through the REST API:

const { data, error } = await supabase.storage
  .from('avatars')
  .createSignedUrl('folder/avatar1.png', 60)

If I want to display a list of users with their avatars, I have to make two requests:

1. get the list of users from supabase (postgrest).
2. get the signed URL for each avatar from supabase.storage.

Both requests eventually query the same database. It would be nice if there was a way to avoid this roundtrip.

Example: If signObjectUrl was implemented in plpgsql, I would expect being able to use it like this:

create table users (
  email text primary key,
  avatar_file text
);

create function avatar_url(users) returns text as
$$
  select storage.signObjectUrl('avatars', $1.avatar_file, 60);
$$;

Then, requesting a list of users, each with a signed URL for their avatar could be retrieved in a single query:

const { data, error } = await supabase
  .from('users')
  .select('email,avatar_url');

My recommendation would be to port most (/all?) of the storage functions to plpgsql and reimplement the storage REST API on top of them.