feat(groups): assign tutor to group

db/init.sql

@@ -182,6 +182,8 @@ CREATE TABLE IF NOT EXISTS users (
   created_at TIMESTAMPTZ DEFAULT now()
 );
 
+ALTER TABLE groups ADD COLUMN IF NOT EXISTS tutor_id INT REFERENCES users(id) ON DELETE SET NULL;
+
 CREATE TABLE IF NOT EXISTS user_branches (
   user_id INT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
   branch_id INT NOT NULL REFERENCES branches(id) ON DELETE CASCADE,