Add credential configuration file support to Google Cloud Hook

[pgagnon]

Add support to authenticate to GCP using a credential configuration file explicitly defined in a connection.

This allows Airflow users to authenticate to GCP using external accounts without relying on the ADC mechanism, allowing the configuration of multiple connections utilizing this mechanism, which offers more flexibility than service account keys.

[ashb]

I'm not too familiar with Google creds, so this might be a stupid q, but how is this student to the key_path option?

[pgagnon]

I'm not too familiar with Google creds, so this might be a stupid q, but how is this student to the key_path option?

@ashb This method is a generalization that supports a wider range of file-based credentials (authorized_user, service_account, external_account, external_account_authorized_user, impersonated_service_account, gdch_service_account), while key_path only supports long-lived service account keys.

[ashb]

Do we need both? Should we deprecated the key one? Can we "just" pass the other types to key_path?

[pgagnon]

@ashb We could probably deprecate it, yes, but:

1. There are just a bunch of cases that I haven't tested related to how we currently handle delegation/impersonation.
2. google.auth.load_credentials_from_file doesn't support passing a JSON dict directly, although we could make it work with a temp file.

[ashb]

Cool let's leave it for now