Specify the behavior of CookieStoreManager.subscribe() when url of subscription is not provided

[szewai]

In step 4.2.2, the spec requests to resolve url with:

Let url be the result of parsing entry["url"] with settings’s API base URL.

This means when entry["url"] is not present, we will use settings's url.

However the existing wpt test verifies service worker registration scope url is used when client does not specify url in option.

What is the expected behavior? @inexorabletash @ayuishii

[szewai]

cc @annevk @RupinMittal