[feature]: Support Google Service Account

### Tell us about the problem you're trying to solve

Google introduced Service Account. It allows access to business resources under company business account istead of using user account authorization.
Service Account once activated and linked to the OAuth application credentials (ClientID and Client Secret) does not require executing token refresh procedure.
In this moment we can't support service account as oauth token exchange flow rejects oAuth authorization request that originates from service account.

### Describe the solution you’d like

We need documentation on how to proceed with service accounts.

In this moment google returns HTTP status ERROR 400 (client bad request) - see attached screenshot. Maybe credentials or user permissions are not configured correctly.

### Describe the alternative you’ve considered or used

i have no alternative

### Additional context

See difference between Service Account and regular OAuth Authorization Code:
https://www.notion.so/bitna-prednost/Connector-testing-apps-credentials-8169679e9328488690d2bc7d78e5ba2a?source=copy_link#28bf8c888cc98098b25de8da75012a4a

Start with the OAuth token exchange flow and the linked Service Account versus regular OAuth Authorization Code reference; verify the credential and user-permission prerequisites described by the issue. Done means documenting the supported Service Account setup and explaining the HTTP 400 failure or its required configuration.

Written by the indexing model from the issue text.