Understand rules for checking HTTP response status code

[lawrence-forooghian]

Currently when we fetch a paginated result we're checking that its status code is 200 and failing if not. This is not specified behaviour and we should formalise it if it's the right thing to do. (I'm not sure if/how the underlying ably-cocoa request method handles response status codes.)

┆Issue is synchronized with this Jira Task by Unito

[lawrence-forooghian]

Have been working on this area a bit in ably-swift recently and the spec is a bit under-specified here; see https://github.com/ably/ably-swift/blob/37bc2aa6b574b05f8f493f6a550e0d60601249c7/Sources/Ably/HTTP/RestResponseContents.swift#L12-L34. We should check how ably-cocoa handles this and decide whether we need any handling ourselves.