Update Glean documentation

[alexgibson]

One-line summary

Updates Glean documentation and links to production dashboards.

Issue / Bugzilla link

N/A

Testing

• pip install -r requirements/docs.txt
• make livedocs

[reemhamz]

r+wc :) gg on the thorough documentation! ✍🏼

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.18%. Comparing base (0ebadb1) to head (94625d2).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14736      +/-   ##
==========================================
- Coverage   77.21%   77.18%   -0.03%     
==========================================
  Files         159      159              
  Lines        8219     8239      +20     
==========================================
+ Hits         6346     6359      +13     
- Misses       1873     1880       +7     

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