Add support for local `plotly.js/` builds to `setup.py`

[ayjayt]

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:

https://github.com/plotly/plotly.py/blob/a8f5ad531643cc3d6132803c6b1d1a5d2f22e8bc/contributing.md?plain=1#L237-L250

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

• [x] 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.
• [x] I have added tests (if submitting a new feature or correcting a bug) or modified existing tests.
• [x] For a new feature, I have added documentation examples in an existing or new tutorial notebook (please see the doc checklist as well).
• [x] I have added a CHANGELOG entry if fixing/changing/adding anything substantial.
• [x] For a new feature or a change in behaviour, I have updated the relevant docstrings in the code to describe the feature or behaviour (please see the doc checklist as well).