Add contributor ladder and architecture docs

[three-foxes-in-a-trenchcoat]

Adds contributor ladder section to GOVERNANCE.md and creates ARCHITECTURE.md with diagram.

[linux-foundation-easycla]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.57%. Comparing base (173e4dc) to head (bbcb368).
⚠️ Report is 221 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1646      +/-   ##
==========================================
+ Coverage   34.76%   43.57%   +8.80%     
==========================================
  Files          94      119      +25     
  Lines        6342     7385    +1043     
==========================================
+ Hits         2205     3218    +1013     
+ Misses       4046     3955      -91     
- Partials       91      212     +121     

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