[MAINT] update PR template to include BEP header

[Remi-Gau]

Closes none

---

• improve readability of PR template message (vertically group list items by topic)
• semantic line break
• add section for BEP PR to include "github admonitions" (started adding those eyetracking BEP and ephys BEP)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.79%. Comparing base (1cb92eb) to head (5545e5c).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1797   +/-   ##
=======================================
  Coverage   87.79%   87.79%           
=======================================
  Files          16       16           
  Lines        1360     1360           
=======================================
  Hits         1194     1194           
  Misses        166      166           

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