`aem` better aemaacs instanceId lookup

[francoisledroff]

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 ....