Address site observability and data access

[chalin]

The goal is to improve website observability. Note that because the site is hosted on Netlify, we have access to Netlify Observability as a fallback for maintainers to cross-check any other implementation.

Alternative approaches

I see these alternatives, out of which we may choose one or more:

• Set up a Collector, and then use it as:
  • Netlify sink
  • A collector for OTel enabled on this website
• For events not naturally in scope of GA, use Netlify edge functions to emit (to the existing GA tag) events for the signals of interest (including fetching events for non .html assets

Why

Improved observability will help us solve a few pending issues including:

• Download URLs #4079
• Analytics for schema files #6230

Tasks

• Add GA4 asset-fetch Edge Function (phase 1) and plan #9555
• Track negotiated Markdown asset fetches with shared GA4 edge analytics #9624
• Adds asset tracking for explicit-path .md and .txt assets, and add cross-function coverage #9627
• Add GA headers to HTTP responses, add live-check fixtures as site test pages #9630
• Document site's analytics, SEO, and observability goals, setup, etc.
• ...