Add download data script

[hoxbro]

Fixes #1325

[hoxbro]

I have built the documents again from this PR. Which fixes the problem in the issue.

[hoxbro]

need to update to work with bokeh_sampledata

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.58%. Comparing base (7c1111c) to head (216bf0e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1326   +/-   ##
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  Coverage   85.58%   85.58%           
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  Files          51       51           
  Lines       11290    11289    -1     
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  Hits         9662     9662           
+ Misses       1628     1627    -1     

[philippjfr]

What's the longer term plan? Should the pyct commands in datashader/__init__.py be removed?

[hoxbro]

What's the longer term plan?

This only collects all the download data procedures in one place, it is heavily focused on the developer experience. pyct is still used.

I think longer term pyct should be replaced by hvsampledata.