Add Plausible analytics to Sphinx documentation #7318

While we direct users to the docs.sentry.io site for usage of our SDK, various examples, etc., we also main a Github pages/Sphinx documentation for the API.

We want to add Plausible to the GH pages site so we can better understand which pages users are visiting most to determine if there are older APIs and functionality that should have dedicated pages on the docs.sentry.io site.