feat: add cawg.metadata label and test.

[gpeacock]

Adds CAWG_METADATA
label and a unit test to ensure it works ok.
We should add a full example later.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.37%. Comparing base (1914df0) to head (3242ee8).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1305      +/-   ##
==========================================
+ Coverage   78.35%   78.37%   +0.01%     
==========================================
  Files         152      152              
  Lines       38811    38815       +4     
==========================================
+ Hits        30412    30420       +8     
+ Misses       8399     8395       -4     

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[scouten-adobe]

@gpeacock I edited the doc comments for the assertion labels. Feel free to merge if you accept those changes.