docs: Fix broken versioning of changelog

[vdusek]

Summary

• Replace manual cp CHANGELOG.md in build scripts with a Docusaurus changelogFromRoot plugin that copies the root changelog to docs/ and all versioned_docs/ at build time
• Remove versioned changelog snapshots from git tracking (gitignored, same as SDK/client repos)
• Update release workflow to exclude changelog from version snapshots
• The current workflow doesn't work anyway

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.31%. Comparing base (e2d7069) to head (b6a4989).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1829      +/-   ##
==========================================
+ Coverage   92.28%   92.31%   +0.02%     
==========================================
  Files         157      157              
  Lines       10889    10889              
==========================================
+ Hits        10049    10052       +3     
+ Misses        840      837       -3     

Flag	Coverage Δ
unit	92.31% <ø> (+0.02%)	⬆️

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