Ayref validator does not support "paper" (PR attached)

[arieleiz]

The plotly documentation specifies that ayref can accept the paper value, as seen in
https://plotly.com/python/reference/layout/annotations/#layout-annotations-items-annotation-ayref.

however the validator does not accept this value. This is a tiny fix that adds "paper" to the validator options:

plotly/plotly.py#4460

[alexcjohnson]

Thanks @arieleiz - this is certainly a bug, but the fix goes in plotly.js, the validator you identified here is the result of codegen from the underlying plotly.js code. I'll transfer the issue and close the PR here.