Manually setting Plotly.js path is not possible with Kaleido v1

[emilykl]

Previously, for image export, it was possible to pass a local path and/or custom URL for Plotly.js by setting pio.kaleido.scope.plotlyjs. This is not documented but it's nonetheless used by our own image test pipeline in Plotly.js.

The following works in Plotly.py v6.0.1, as well as v6.1.2 with Kaleido v0:

import plotly.io as pio

pio.kaleido.scope.plotlyjs = "path/to/local/plotly.js"

But with Plotly.py v6.1.2 and Kaleido v1 it gives the following error:

AttributeError: 
Attribute plotly.io.defaults.plotlyjs is not valid.

IMO there's no reason to stop supporting this option and it should be relatively straightforward to pass through into Kaleido v1.