[DOCS] Complete setup guide for googleAnalyticsR

[bart-turczynski]

Across the last few years, I wanted to use googleAnalyticsR, but failed to get it working. The searchConsoleR set up is always a breeze. For GA, I seem to be running into some issue with getting access either b/c I don't know how to correctly setup Google Cloud APIs or there's some weird clash with other credentials? I keep running into 403 errors despite being an admin, setting up service accounts, using OAuth, adding service account emails to GA4 as well... Where can I find information re: setting up the very basics? All guides seem to start with run OAuth, use GA4; the more detailed guides seem to be outdated or missing from the web.