feature #4: create procedure for user

resources/functions/user/find_user_by_username.sql

@@ -0,0 +1,12 @@
+create or replace procedure find_user_by_username(in username text, inout resource json) language plpgsql as
+$$
+declare
+    _username alias for username;
+begin
+    select to_json(u) into resource
+    from "user" as u
+    where u.username = _username;
+end;
+$$;
+
+-- drop procedure if exists find_user_by_username(text, inout json);