[ENH] Add admonitions to task and beh pages

[Remi-Gau]

• Blocked by [ENH] add an entry to behavioral datasets to listing of datasets bids-examples#431

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• add some admonitions to task and behavioral pages
• implement semantic line break in a few places
• change some wording / capitalization (e.g should --> SHOULD)

[Remi-Gau]

switched to using MAY here

[Remi-Gau]

when playing around with this I realized that macros should not be put into admonitions other wise the output won't be what you expect.

Will mention in the contributing doc.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.93%. Comparing base (943c20e) to head (62c71d3).
Report is 16 commits behind head on master.

❗ Current head 62c71d3 differs from pull request most recent head 440cbf0. Consider uploading reports for the commit 440cbf0 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1735   +/-   ##
=======================================
  Coverage   87.93%   87.93%           
=======================================
  Files          16       16           
  Lines        1351     1351           
=======================================
  Hits         1188     1188           
  Misses        163      163           

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[Remi-Gau]

to view:

• task page: https://bids-specification--1735.org.readthedocs.build/en/1735/modality-specific-files/task-events.html
• behavioral page: https://bids-specification--1735.org.readthedocs.build/en/1735/modality-specific-files/behavioral-experiments.html