Persisting presets defined with prebuilds to DB

Signed-off-by: Danny Kopping <danny@coder.com>

coderd/database/migrations/000292_system_user.up.sql

@@ -0,0 +1,6 @@
+ALTER TABLE users
+	ADD COLUMN is_system bool DEFAULT false;
+
+CREATE INDEX user_is_system_idx ON users USING btree (is_system);
+
+COMMENT ON COLUMN users.is_system IS 'Determines if a user is a system user, and therefore cannot login or perform normal actions';