Refactor Ably wrapper to fail early when trying to call a method while the required channel is not created

[KacperKluka]

As noticed here, we have a few methods in the Ably wrapper that accept a callback and need an already created channel (e.g. sendEnhancedLocations()). Currently, if we call those methods while there is no channel created for the given trackable ID, they will do nothing and call the callback with a success. Instead, we would like them to fail early and call the callback with an error.

[deanna-lad]

The corresponding Jira issue is https://ably.atlassian.net/browse/SDK-1338