Update colorspaces.py add CMYK

[HaleySchuhl]

add logic for additional colorspaces in visualization plot

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Type of update
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• feature enhancement
• Work in progress

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• PR functionality reviewed in a Jupyter Notebook
• All tests pass
• Test coverage remains 100%
• Documentation tested
• New documentation pages added to plantcv/mkdocs.yml
• Changes to function input/output signatures added to updating.md
• Code reviewed
• PR approved

[codecov]

Codecov Report

Merging #1390 (167bd0f) into main (1d5efc8) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1390   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files          158       158           
  Lines         6934      6940    +6     
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+ Hits          6934      6940    +6     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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Files	Coverage Δ
plantcv/plantcv/rgb2gray_cmyk.py	100.00% <100.00%> (ø)
plantcv/plantcv/visualize/colorspaces.py	100.00% <100.00%> (ø)