Service Directory: auto data detection

[asimpleidea]

Just as it currently happens with the Cloud Metadata feature, where the operator automatically detects the platform, network and sub-network where it is running -- e.g. GKE, a new feature will be introduced that automatically infers the Region and Project ID in case the cluster is GKE.

To do this write auto as a value, e.g.:

projectID: auto
defaultRegion: auto

I'd prefer to do it with an explicit auto rather than keeping them empty and just try it anyways, but I will welcome different opinions and feedback! :)