Support both the Kaleido v0 and v1 APIs in Plotly.py.

• Updatefig.write_image(),fig.to_image(),pio.write_image(), andpio.to_image() to work with both Kaleido versions
• Add deprecation warnings for:
  • theengine argument toto_image() andwrite_image()
  • Use of Orca
  • Use of Kaleido v0
  • Setting defaults viakaleido.scope.*
• Add a new way of setting image export defaults:plotly.io.defaults.*. This can be used in place ofkaleido.scope.* and supports all the same settings:default_format,default_height,default_width,default_scale,mathjax, andtopojson.pio.defaults is backwards-compatible with Kaleido v0.
• Addpio.write_images() function for generating multiple images at a time
  • Required due to the new Kaleido architecture;much faster than callingwrite_image() in a loop
  • Addpio.get_chrome() function which wrapskaleido.get_chrome_sync(), and add a CLI entry pointplotly_get_chrome for installing Chrome from the command line
• Updatetests/test_optional/test_kaleido/test_kaleido.py tests to work with either Kaleido v0 or v1. They now also actually check that an image of the right format and dimensions has been generated, as opposed to using mocking to check that the right arguments are being passed to Kaleido.
• Add test forpio.write_images()
• Update CI to run all tests with Kaleido v1, and add an additional job which runs the Kaleido tests with Kaleido v0, to protect against regressions

TODO

• Update CI to run all tests with Kaleido v1
• Add CI job to run Kaleido tests with Kaleido v0
• Finalize UX for what happens if Chrome is not found
• Finalize UX / API for EPS
• Figure out what to do about 'renderers' Kaleido test
• Add deprecation warning forengine argument towrite_image /to_image
• Re-add removed Orca support but with DeprecationWarning
• Fix DeprecationWarnings not showing up
• Expose API for setting defaultmathjax andtopojson