Restore delegate_to param in GoogleDiscoveryApiHook

[austinletson]

Restore delegate_to param to GoogleDiscoveryApiHook to allow to specification of a service account for domain-wide delegation when using GoogleDiscoveryApiHook to access Google APIs which support domain-wide delegation but do not have a dedicated hook (such as Workspaces Admin API).

Note that based on the discussion in #9461, the delegate_to param was deprecated in #29088 (and removed in #30748) from many hooks including GoogleDiscoveryApiHook. However, the delegate_to param was not removed from the docstring for the GoogleDiscoveryApiHook constructor.

Update GCP connection docs to reflect delegate_to param in GoogleDiscoveryApiHook usage only when using Google APIs that support domain-wide delegation.

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[eladkal]

cc @shahar1 can you please review?

[shahar1]

Well reasoned, LGTM

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