[ENH] Add admonitions to task and beh pages

[Remi-Gau]

• Blocked by https://github.com/bids-standard/bids-examples/pull/431

• 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]

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[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 (62c71d3). Report is 16 commits behind head on master.

:exclamation: 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

```diff @@ 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