Add a gallery example for regional manifold extraction

[ESadek-MO]

Closes #1285.

Create a suitable region manifold extraction example:

• Agree the geovista.examples category into which to create the example
• Generate and add example test asset to the geovista-data repository
• Update our pooch registry.txt and associated DATA_VERSION
• Ensure that the new asset is downloaded, see geovista download
• Ensure the visual tests pass pytest -m example

[bjlittle]

Reference:

• added regional manifold example geovista-data#70
• Renamed image test image "regional_mani" to "wedge_manifold" geovista-data#71
• new image for wedge_manifold geovista-data#72

[codecov]

Codecov Report

Attention: Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.63%. Comparing base (31334fe) to head (ded31a1).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/geovista/examples/extraction/wedge_manifold.py	96.77%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1284      +/-   ##
==========================================
+ Coverage   91.34%   91.63%   +0.29%     
==========================================
  Files          58       59       +1     
  Lines        2959     2990      +31     
==========================================
+ Hits         2703     2740      +37     
+ Misses        256      250       -6     

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[ESadek-MO]

All failing tests should pass once bjlittle/geovista-data#71 is merged in!

[bjlittle]

@ESadek-MO Awesome! Thanks for hanging in there, really appreciated 💯

Just some minor suggestions then we're good to go 🚀

[bjlittle]

@all-contributors please add @ESadek-MO for code and example and data

[allcontributors]

@bjlittle

I've put up a pull request to add @ESadek-MO! 🎉