Treat 503 as an expected authentication response

This avoids spamming error reports on a 503 and instead uses the auth
failure delay mechanism which will reduce the load we create on the API
and also on openvpn from reconnect attempts and help reduce subsequent
503s and other slowness

Change-type: patch

Author: Page-

src/api.ts

@@ -53,7 +53,7 @@ const checkDeviceAuth = memoize(
 			url: `${BALENA_API_INTERNAL_HOST}/services/vpn/auth/${username}`,
 			...getPassthrough(`Bearer ${password}`),
 		});
-		if ([200, 401, 403].includes(statusCode)) {
+		if ([200, 401, 403, 503].includes(statusCode)) {
 			return statusCode;
 		}
 		throw new Error(`Unexpected status code from the API: ${statusCode}`);