Add ColorMap widget

[philippjfr]

Adds ColorMap widget which was recently added to Bokeh.

• Implements Colormap widget #5154
• Add docs
• Add tests
• Add reference gallery image

[codecov]

Codecov Report

Merging #5647 (db5c7d0) into main (a557079) will decrease coverage by 57.74%.
The diff coverage is 35.29%.

@@             Coverage Diff             @@
##             main    #5647       +/-   ##
===========================================
- Coverage   81.89%   24.16%   -57.74%     
===========================================
  Files         288      288               
  Lines       41812    41878       +66     
===========================================
- Hits        34243    10118    -24125     
- Misses       7569    31760    +24191     

Flag	Coverage Δ
ui-tests	?
unitexamples-tests	24.16% <35.29%> (-49.53%)	⬇️

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Files	Coverage Δ
panel/widgets/__init__.py	100.00% <ø> (ø)
panel/pane/ipywidget.py	43.37% <50.00%> (-5.38%)	⬇️
panel/tests/widgets/test_select.py	17.09% <21.73%> (-82.91%)	⬇️
panel/widgets/select.py	35.71% <41.46%> (-59.08%)	⬇️

... and 220 files with indirect coverage changes

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[tupui]

Oh nice 👏 I actually needed something like that and went the route of generating a colormap from a single color. This is way simpler and complete as you really take advantage of existing colormaps. Still in case you are wondering:

https://github.com/Simulation-Decomposition/simdec-python/blob/256afac0a8b9d03dc72398533274cd10bd8446f6/src/simdec/visualization.py#L37-L70