[S3] Support getting the fully qualified path (URL/URI) to the object

[daniel-abramov]

Currently, when the user tries to list the objects inside the bucket, we get a result that contains the list of objects with their corresponding metadata. The key of each object is contained in the result, however there seems to be no way to get the fully-qualified URL/URI to the object in a format https://{ENDPOINT}/{BUCKET}/{OBJECT} (if we're talking about path-style URLs).

It would be nice if there was a way to introduce a method for the Object or something similar that would allow the user to get the URL of the object (in both path-style and subdomain-style format). Otherwise the only way for user to do it is to store the endpoint etc somewhere else and have a function in a user code that does it. Not a big deal, however since the information about the endpoint and region is anyway part of the client and used to perform requests, maybe we could at least add methods to access them, so that the information is not duplicated.