Implement cross-domain tracking across subsites

[cjyabraham]

We currently have UA properties for each subsite but not GA4 properties:

• [x] https://community.cncf.io/
• [x] https://jobs.cncf.io/
• [x] https://contribute.cncf.io/
• [x] https://glossary.cncf.io/
• [x] https://landscape.cncf.io/
• [x] http://store.cncf.io/

Implement cross-domain tracking using our CNCF GA4 property so that we can see usage across the whole CNCF web ecosystem and also within each subsite.

Add traffic metrics across each subsite to the monthly analytics report.

[cjyabraham]

done