Important links for this POC
https://stackoverflow.com/questions/49480940/app-engine-custom-domain-with-service
https://cloud.google.com/appengine/docs/standard/python/mapping-custom-domains
https://www.murrayc.com/permalink/2017/10/15/google-app-engine-using-subdomains/
https://groups.google.com/forum/#!msg/google-appengine/xycWwRX2OiU/8ivTxBrDAgAJ
execute the command gcloud app domain-mappings create domain_name
Add the ipv4 and ipv6 values in registered hosts section in google domains and add name with ghs.googlehosted.com to record set of cname type