Can some one please help me understand how can we share own custom metrics( variable/attribute) from adobe campaign to adobe analytics with KPI sharing feature (apart from OOB metrics like open, click etc)?
At present, there is no want to do this with the OOB KPI sharing workflows in ACS. Maybe this changes in the future.
What you can do now, is add parameters to the link tracking from within the Brand configurations and capture these URL parameters in AA to track and tag the visitors coming from an Email click through.
Check out the page on how to add Brand and UTM parameters in ACS: Branding