Add Tabulator.sortable parameter

[philippjfr]

Adds control over the header sort of the Tabulator.

• Add docs
• Add tests

[codecov]

Codecov Report

Merging #5827 (cd86e6b) into main (b21b740) will decrease coverage by 0.04%.
Report is 15 commits behind head on main.
The diff coverage is 94.73%.

@@            Coverage Diff             @@
##             main    #5827      +/-   ##
==========================================
- Coverage   72.37%   72.34%   -0.04%     
==========================================
  Files         290      290              
  Lines       42214    42296      +82     
==========================================
+ Hits        30554    30598      +44     
- Misses      11660    11698      +38     

Flag	Coverage Δ
unitexamples-tests	72.34% <94.73%> (-0.04%)	⬇️

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Files	Coverage Δ
panel/tests/widgets/test_tables.py	99.80% <100.00%> (+<0.01%)	⬆️
panel/widgets/tables.py	87.62% <91.30%> (+0.07%)	⬆️

... and 16 files with indirect coverage changes

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[philippjfr]

UI test failures appear unrelated. Will fix those separately today.