Impersonate instead of downloading SA keys

[rickygodoy]

According to documentation, it's needed to create a service account and have it downloaded to local machine, which pose a major risks to the solution and bad example to follow.

A solution would be to impersonate the service account in order to prevent accidents. Would be great to be able to run with local logged user instead of only service accounts. Also use ADC to authenticate (https://cloud.google.com/docs/authentication/application-default-credentials).

That would make the solution more secure and easy to run!