feat(grouping): add onPreHeaderContextMenu for Column Picker usage

[ghiscoding]

• adding new events onPreHeaderContextMenu and onPreHeaderClick which is mostly to be able to open the Column Picker from either the regular column headers OR the Column Group from the Pre-Header when defined
• also works with/without frozen column
• Note: before calling the column picker, we need to make sure that the pre-header target element is in fact a column group, because if it's anything then we shouldn't open the column picker (e.g. draggable grouping dropzone)

TODOs

• add unit tests
• add Cypress tests

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.8%. Comparing base (e5f00c1) to head (9fe3d2d).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1580     +/-   ##
========================================
+ Coverage    99.8%   99.8%   +0.1%     
========================================
  Files         198     198             
  Lines       21764   21773      +9     
  Branches     7148    7010    -138     
========================================
+ Hits        21703   21712      +9     
- Misses         55      61      +6     
+ Partials        6       0      -6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.