Add support for impersonation in GCP hooks

[olchas]

Adding support for direct account impersonation in GCP hooks. First part of changes to address #8803

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[boring-cyborg]

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[olchas]

@mik-laj, @ad-m, could you take a look?

[boring-cyborg]

Awesome work, congrats on your first merged pull request!

[potiuk]

🎉 🎉 🎉 🎉 🎉 🎉 🎉 🎉 🎉 🎉 🎉 🎉

[ad-m]