WEBDEV-7037 Add collection_layout metadata field

[rebecca-shoptaw]

Adds a collection_layout field to metadata, for use in the new custom collections.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 70.81%. Comparing base (52502aa) to head (c37b9e2).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/models/metadata.ts	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #3      +/-   ##
==========================================
- Coverage   71.01%   70.81%   -0.20%     
==========================================
  Files          17       17              
  Lines        1128     1134       +6     
  Branches       19       19              
==========================================
+ Hits          801      803       +2     
- Misses        325      329       +4     
  Partials        2        2              

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[latonv]

LGTM, just noting version change.