Add Impersonate Service Account argument

[wintermi]

This PR adds an --impersonate-service-account argument to the run and test commands, along with the required changes to allow for the impersonation of service accounts without the need to change ADC or call gcloud

This would resolve issue #2000 and would be an alternative to solution than PR #2001

Impersonation could then be achieved by executing:

dataform run --impersonate-service-account=<sSERVICE_ACCT_EMAIL>

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[camilleAmaury]

+1, this would enable to use impersonation in CI rather than giving the rights directly to the CI service account. There is no way to workaround that currently.

[kolina]

/gcbrun

[kolina]

Sorry for the late review. A couple of things:

• Integration tests are failing, can you take a look at fixing them? Now we have a guide of running them locally
• Let's resolve conflicts