[ENH] add `matches` and `source_entity` to glossary

[Remi-Gau]

• closes #1748

• https://bids-specification--1781.org.readthedocs.build/en/1781/glossary.html#matches-entities

• https://bids-specification--1781.org.readthedocs.build/en/1781/glossary.html#source_entities-entities

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• [ ] improve filenaming templates with those placeholders to link to glossary.
• [ ] link to glossary when they occur in text
• [x] ensure that entities pages are not affected

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 87.93%. Comparing base (943c20e) to head (5bf2cc4).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1781   +/-   ##
=======================================
  Coverage   87.93%   87.93%           
=======================================
  Files          16       16           
  Lines        1351     1351           
=======================================
  Hits         1188     1188           
  Misses        163      163           

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