Documentation: Update use case thumbnails to match updated flow diagram

[georgemccabe]

The latest MET flowchart has some updates to the color scheme:
https://github.com/dtcenter/MET/blob/develop/docs/Flowchart/MET_flowchart_v12.1.0.png

The met_tool_wrapper use cases could be updated so that the thumbnails match the new format.
View the thumbnails here: https://metplus.readthedocs.io/en/develop/generated/met_tool_wrapper/index.html
They are stored in docs/_static.

Describe the Task

Here is what would need to change:

• EnsembleStat is half green half blue, should be light blue
• GenEnsProd is dark green, should be light green
• GenVxMask is dark green, should be light green
• PCPCombine is dark green, should be light green
• PlotDataPlane is puke green, should be orange
• PlotPointObs is dark green, should be orange
• Point2Grid is dark green, should be pink
• RegridDataPlane is dark green, should be pink
• All of the blue ovals should be light blue

Time Estimate

~1 day

Sub-Issues

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Relevant Deadlines

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Funding Source

PRJ014253 NOAA METPLUS SW

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Define Related Issue(s)

Consider the impact to the other METplus components.

• METplus, MET, METdataio, METviewer, METexpress, METcalcpy, METplotpy

Task Checklist

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• Complete the issue definition above, including the Time Estimate and Funding Source.
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