docs: Refresh README.md and point other docs to admin repo

[misteroneill]

Description

This is a long-needed update to the Video.js README. Also, other docs are now pointing to files in the videojs/admin repo.

Specific Changes proposed

• Refresh Video.js README.
  • Removes the old discussion of the Google Analytics tracking pixel in vjs.zencdn.net-hosted versions prior to 7.0.0. The last version that included this was 6.13.0, which was 6 years ago. That seems like enough time to consider the issue dead. Also, Google Analytics likely no longer collects that data as it has moved on from the Universal Analytics API.
• The following docs are moved to the videojs/admin repo, but the files are kept here and link to the replacements for discoverability:
  • CODE_OF_CONDUCT.md
  • COLLABORATOR_GUIDE.md
  • CONTRIBUTING.md

Requirements Checklist

• Feature implemented / Bug fixed
• Reviewed by Two Core Contributors

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.18%. Comparing base (73db132) to head (0f10a65).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8837   +/-   ##
=======================================
  Coverage   83.18%   83.18%           
=======================================
  Files         120      120           
  Lines        8047     8047           
  Branches     1931     1931           
=======================================
  Hits         6694     6694           
  Misses       1353     1353           

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[amtins]

LGTM 👍🏽