Support for MathJax and HTML entities in parcoords dimension labels

[cpsievert]

Is this a known limitation? I can get a more minimal (JS) example if need be

plot_ly(
    type = 'parcoords',
    dimensions = list(
        list(range = range(iris$Sepal.Width),
             label = TeX('Sepal Width \\alpha'), values = iris$Sepal.Width),
        list(range = range(iris$Sepal.Length),
             label = '<b>Sepal Length</b>', values = iris$Sepal.Length),
        list(range = range(iris$Petal.Width),
             label = 'Petal Width', values = iris$Petal.Width),
        list(range = range(iris$Petal.Length),
             label = 'Petal Length', values = iris$Petal.Length)
    )
) %>% 
    layout(title = TeX("\\text{Some mathjax: }\\alpha+\\beta x")) %>% 
    config(mathjax = "cdn")

Requested in plotly/plotly.R#1298

[etpinard]

related: #2292