Handle nodata option for rasterized RGB image

[hoxbro]

Fixes holoviz/hvplot#1091

This will make it possible to do the following:

import hvplot.xarray  # noqa
import xarray as xr
import rioxarray as rxr

rgb_data = xr.load_dataarray("/home/shh/Downloads/sentinel2_seattle.nc")
rgb_data = xr.load_dataarray("https://github.com/ivandorte/datasets_samples/raw/main/sentinel2_seattle.nc")
rgb_plot = rgb_data.hvplot.rgb(x="x", y="y", bands="band", rasterize=True, tiles="OSM")
rgb_plot + rgb_plot.redim.nodata(R=0)

cog_url = "/home/shh/Downloads/5d7dad0becaf880008a9bc89.tif"
cog_url = "https://oin-hotosm.s3.amazonaws.com/5d7dad0becaf880008a9bc88/0/5d7dad0becaf880008a9bc89.tif"
da = rxr.open_rasterio(cog_url)
plot = da.hvplot.rgb(x="x", y="y", rasterize=True, tiles=True)
plot + plot.redim.nodata(R=0)

Todo:

• Add test
• Maybe automatically detect nodata in xarray DataArray/Dataset (this could be done in hvplot)

[codecov-commenter]

Codecov Report

Merging #5774 (f03b135) into main (a12e33a) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #5774   +/-   ##
=======================================
  Coverage   88.15%   88.16%           
=======================================
  Files         307      307           
  Lines       62908    62930   +22     
=======================================
+ Hits        55457    55480   +23     
+ Misses       7451     7450    -1     

Flag	Coverage Δ
ui-tests	22.39% <8.33%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
holoviews/plotting/bokeh/raster.py	83.19% <100.00%> (+0.28%)	⬆️
holoviews/tests/element/test_raster.py	100.00% <100.00%> (ø)
holoviews/tests/plotting/bokeh/test_rasterplot.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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