Improve error message when CDAP cannot connect to public Cloud SQL instance.
Cloud SQL instance need to be configured with authorize networks as 0.0.0.0/0 when setup with public IP.
This is required when CDAP system services are running on un-known/ephemeral public IPs (for example on public kubernetes cluster).
Cloud SQL plugin can determine if the cloud sql instance it is trying to connect to is public or private. If connection to the public cloud sql instance fails, the error message can be more descriptive asking user to check the authorize networks. In fact we can possibly query authorize networks from public cloud sql and ask user to add 0.0.0.0/0 if its not there.
Similar handling and error messaging should be done for wrangler, however it might be bit involved there since wrangler backend is more generic but UI is specialized. Possibly UI can query authorized networks in this case.
Plugin doc should also be updated as a part of this change.