add official exercises to the database

migrations/20241210224609_official_exercises.sql

@@ -0,0 +1,7 @@
+-- Add migration script here
+
+ALTER TABLE exercises 
+ADD COLUMN official BOOLEAN NOT NULL DEFAULT FALSE,
+ADD COLUMN author_id UUID REFERENCES users(id),
+ADD COLUMN description TEXT,
+ADD COLUMN created_at TIMESTAMP NOT NULL DEFAULT NOW();