Hi, this PR adds a --local= flag to setup.py updateplotlyjsdev so we don't need to use circleci to use our custom plotly.js w/ plotly.py.

This helps a little bit with community dev flow, I think.

Here is the docs:

Thanks!

edit: could probably be made to work with github repos too with a little fetch here and there

Code PR

This is a small addition to the build system, not a change to plotly.py as such

• I have read through the contributing notes and understand the structure of the package. In particular, if my PR modifies code of plotly.graph_objects, my modifications concern the codegen files and not generated files.
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  new tutorial notebook (please see the doc checklist as well).
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