Add Service Account impersonation in GCP as a new authentication method

[sergargar]

New feature motivation

Add service account impersonation in GCP as a new authentication method in Prowler.

Solution Proposed

Adding the flag --impersonate-service-account <target service account email>

Describe alternatives you've considered

Instead of saving credentials file or run prowler inside GCP workload (for the metadata server option), add the mentioned authentication method.
This is actually security best practice so it should be high priority because now the credentials.json approach have private keys on the machines which is not a good idea.

Additional context

Thanks to Ben Lahav via Slack for the idea!