docs: add GA4 README tracking pixels

[ScriptedAlchemy]

Summary

• add GA4 README tracking pixels using measurement ID G-DRPXW0EEVT to every README.md in the repo
• replace the existing stale Universal Analytics README pixels where they were present
• include both ep.example and ep.readme_path so Analytics can report by top-level example family and exact README path

Validation

• checked all README.md files: readmeCount=152, issueCount=0
• every tag has tid=G-DRPXW0EEVT, en=readme_view, ep.repository=module-federation-examples, ep.example, and ep.readme_path
• no old ssl.google-analytics.com/collect, UA-120967034-1, ga-beacon, or google-analytics.com/collect Markdown pixels remain
• git diff --check