feat: Add {x,y}gap parameter to heatmaps #151

Job	Run time
Tests (ubuntu-latest, chrome, plotly_ndarray,plotly_image,static_export_default,debug)	3m 38s
Build Wasm Examples (callback-example)	58s
Rustfmt	16s
Clippy	4m 32s
Code Coverage	13s
Build Examples (customization/density_mapbox_example)	25s
Tests (macos-latest, chrome, plotly_ndarray,plotly_image,static_export_default,debug)	7m 37s
Build Examples (maps)	1m 17s
Build Book	3m 53s
Build Examples (custom_controls)	53s
Build Examples (financial_charts)	40s
Build Examples (customization/consistent_static_format_export)	1m 45s
Build Wasm Examples (basic)	1m 1s
Build Examples (images)	54s
Build Examples (ndarray)	32s
Build Examples (scientific_charts)	33s
Tests (windows-latest, chrome, plotly_ndarray,plotly_image,static_export_chromedriver,debug)	9m 59s
Build Examples (basic_charts)	42s
Build Examples (customization/multiple_plots_example)	33s
Build Examples (shapes)	46s
Build Examples (kaleido)	1m 18s
Tests (ubuntu-latest, firefox, plotly_ndarray,plotly_image,static_export_geckodriver,static_expor...	3m 29s
Build Examples (3d_charts)	38s
semver	47s
Build Examples (statistical_charts)	41s
Build Examples (subplots)	27s
Build Examples (themes)	28s
	48m 55s

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