Experiment with TOC in solr

[cdrini]

Closes #

Technical

• Add a new chapter field to solr and populate it on the edition level with the toc data in markdown format
• On the work level, set it to the unsorted set of all its editions chapters.
• RISK: This is a lot of new data in solr, and duplicated! Could cause bloat/perf issues
• RISK: We use the work-level highlighting to display the toc in the search view, but we don't know which book the toc entry came from... Might need to include some edition data in there.
• Add ability to see matching subjects to search page
• Add ability to see matching chapters to search page
• Special deploy: Need to add the new chapters field to solr. This can be done via the solr UI. Note this of course won't backfill the data, a full reindex is needed for that, but that will make it possible to merge/deploy this without needing the solr_next flag.

Testing

Screenshot

Stakeholders

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 17.05%. Comparing base (ce16a79) to head (3229519).
Report is 444 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9898      +/-   ##
==========================================
+ Coverage   16.06%   17.05%   +0.99%     
==========================================
  Files          90       89       -1     
  Lines        4769     4725      -44     
  Branches      832      829       -3     
==========================================
+ Hits          766      806      +40     
+ Misses       3480     3409      -71     
+ Partials      523      510      -13     

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