add downsampling example using minmaxlttb-rs #93

Job	Run time
Rustfmt	15s
Clippy	3m 49s
Build Wasm Examples (callback-example)	56s
semver	37s
Build Wasm Examples (basic)	1m 3s
Build Book	3m 26s
Tests (ubuntu-latest, chrome, plotly_ndarray,plotly_image,static_export_default,debug)	2m 56s
Tests (ubuntu-latest, firefox, plotly_ndarray,plotly_image,static_export_geckodriver,static_expor...	3m 10s
Code Coverage	12s
Tests (windows-latest, chrome, plotly_ndarray,plotly_image,static_export_chromedriver,debug)	6m 6s
Tests (macos-latest, chrome, plotly_ndarray,plotly_image,static_export_default,debug)	2m 49s
Build Examples (custom_controls)	35s
Build Examples (customization/consistent_static_format_export)	1m 20s
Build Examples (customization/density_mapbox_example)	36s
Build Examples (customization/multiple_plots_example)	35s
Build Examples (images)	40s
Build Examples (ndarray)	33s
Build Examples (basic_charts)	36s
Build Examples (financial_charts)	30s
Build Examples (kaleido)	1m 18s
Build Examples (maps)	45s
Build Examples (scientific_charts)	29s
Build Examples (themes)	34s
Build Examples (statistical_charts)	32s
Build Examples (shapes)	28s
Build Examples (3d_charts)	31s
Build Examples (subplots)	24s
	35m 45s

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