Add support for overplotting a ocean/land mask with GeoMakie

[Sbozzolo]

This commit adds support for applying land/sea masks to GeoMakie plots. The masks are obtained directly from GeoMakie as a collection of polygons. For the ocean mask, we use bathymetry data at 0 elevation. Data is provided by
NaturalEarth.jl. (I had to bump the minimum compat for GeoMakie to 0.7 because support NaturalEarth.jl was introduced in that release.)

This new option is only aesthetics: it does change the underlying data (we simply overplot something else). This also means that the colorbar will include values under the mask. Applying the mask directly to the data is left for future work.

Thanks @haakon-e for help with this feature.

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 16.84%. Comparing base (0a024c7) to head (b2da5d8).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
ext/ClimaAnalysisGeoMakieExt.jl	75.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #72       +/-   ##
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- Coverage   96.35%   16.84%   -79.51%     
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  Files           9        9               
  Lines         548      558       +10     
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- Hits          528       94      -434     
- Misses         20      464      +444     

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[AlexisRenchon]

oooh that's cool!!

[AlexisRenchon]

"Applying the mask directly to the data is left for future work"

we could make it a clear outlier and use lowclip or highclip in the heatmaps, then build the colorbar without outlier (by building it independently), e.g.

ax, hm = heatmap(fig[1, 1], xs, ys, zs, colormap = :something,
    colorrange = (-x, y), lowclip = :blue)
Colorbar(fig[1, 4], limits = (-x, y), colormap=:something)

https://docs.makie.org/stable/reference/blocks/colorbar#colorbar

[Sbozzolo]

"Applying the mask directly to the data is left for future work"

we could make it a clear outlier and use lowclip or highclip in the heatmaps, then build the colorbar without outlier (by building it independently), e.g.

ax, hm = heatmap(fig[1, 1], xs, ys, zs, colormap = :something,
    colorrange = (-x, y), lowclip = :blue)
Colorbar(fig[1, 4], limits = (-x, y), colormap=:something)

https://docs.makie.org/stable/reference/blocks/colorbar#colorbar

My plan is to create an OutputVar from a land/sea mask so that it can be used beyond plotting.