`aem` better aemaacs instanceId lookup

When aem is registering as an Adobe I/O Event provider
we need to uniquely identify skyline author clusters at runtime

we‘ve been using the `author` externalizer service to compute the root url.
as it is matching the skyline author's environment public url

We believe we could do a better more user friendly job here to name this and label this environment.
May be relying on pre-populated Cloud Manager environment variables ....

No file or test is identified. Start by tracing aem registration as an Adobe I/O Event provider and the current author externalizer service used to compute the root URL; clarify the required instanceId and environment-label behavior. The work is done when Skyline author clusters are uniquely identified at runtime with a user-friendly environment name.

Written by the indexing model from the issue text.