Provide some documentation for project on how they can embed GA on their website

With PHP support for projects being deprecated, our GDPR documentation is becoming outdated: https://www.eclipse.org/eclipse.org-common/themes/solstice/docs/#gdpr.

@oliviergoulet, I’d like us to migrate this documentation to Storybook and update it with best practices for projects to embed web analytics on their websites. The docs should ensure that analytics are only embedded if the user has accepted our cookie consent banner.

While GTM is currently the recommended solution for projects, I would like us to explore a simpler built-in solution where projects can add their GA ID in their Hugo config file, and we handle the cookie consent check and embedding process automatically for them.

This need became clear to me while I was assisting @mmaiero with this issue: eclipsefdn/hosted-services-privacy-and-acceptable-usage-policy#1 (comment 2954042).