Add Google Analytics tracking to the frontend docs site

[vanitabarrett]

What

This work looks at adding Google Tag Manager and Google Analytics on frontend.design-system.service.gov.uk. This follows on from work to add it to the design system: alphagov/govuk-design-system#1610. Ideally this uses the same cookie and we make use of sub-domain consent.

Why

We want to include GA on tracking back on the Frontend Docs site so that we can better understand how our users are engaging with the website. We can then use this data to learn and improve more about the Frontend Docs.

Who needs to know about this

Developers, Performance Analyst, Content Designer

Done when

Tasks

• Decide approach for sub-domain consent govuk-design-system#1613
• How does this affect our GTM setup and deployment plan?
• Tweak existing govuk-design-system cookie consent functions to handle sub-domain consent
• Add cookie consent functions in the frontend docs #118
• Add Google Tag Manager code to the frontend docs #119
• Add cookie banner to frontend docs #134
• Change content within the design system cookie page
• Change content within the design system cookie banner
• Reset the banner for users if switching from design-system only consent to sub-domain consent