Documentation - OAuth Client Credentials (internal) available only for G-Suite users

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One of the necessary steps to use this plugin is creating [OAuth Client Credentials](https://matomo.org/docs/google-analytics-importer/#1-creating-google-oauth-client-config). The tutorial instructs user to choose "[interal](https://img.matomo.org/spai/w_832+q_lossless+ret_img+to_webp/https://static.matomo.org/wp-content/uploads/2019/07/oauth-type-2.png)" type, but it is (now) available only to G-Suite users. Other Google users can choose only "external" type, which comes with some limitations:

> In this mode, your app is available to any user with a Google Account. External apps that request sensitive or restricted user data must first be verified by Google. This process may take 4–6 weeks. In addition, if you selected restricted scopes, you'll need to go through an independent security review, which can cost $15k–$75k.

The documentation should mention in [Requirements](https://matomo.org/docs/google-analytics-importer/#requirements) chapter the need for G-Suite account.

Start with the Google Analytics Importer documentation's Requirements chapter and review the linked OAuth Client Credentials tutorial. Update the requirements to state that a G-Suite account is needed for the internal OAuth type, and ensure the limitation for other Google users is accurately represented.

Written by the indexing model from the issue text.