feat: purge expired api keys in dbpurge (#20863)

closes https://github.com/coder/coder/issues/19889

This is in response to a migration in v2.27 that takes very long on deployments with large `api_key` tables.

coderd/database/queries/apikeys.sql

@@ -85,6 +85,26 @@ DELETE FROM
 WHERE
 	user_id = $1;
 
+-- name: DeleteExpiredAPIKeys :one
+WITH expired_keys AS (
+	SELECT id
+	FROM api_keys
+	-- expired keys only
+	WHERE expires_at < @before::timestamptz
+	LIMIT @limit_count
+),
+deleted_rows AS (
+	 DELETE FROM
+		 api_keys
+	 USING
+		 expired_keys
+	 WHERE
+		 api_keys.id = expired_keys.id
+	 RETURNING api_keys.id
+ )
+SELECT COUNT(deleted_rows.id) AS deleted_count FROM deleted_rows;
+;
+
 -- name: ExpirePrebuildsAPIKeys :exec
 -- Firstly, collect api_keys owned by the prebuilds user that correlate
 -- to workspaces no longer owned by the prebuilds user.