Add support for histfunc='kde' in px.histogram()

[janosh]

Would be great if the histfunc argument of px.histogram() accepted 'kde'. It's currently limited to ['count', 'sum', 'avg', 'min', 'max'] but I'm looking for output like what figure_factory.create_distplot() gives when show_hist=False, show_rug=False.

import plotly.figure_factory as ff
import numpy as np

x1 = np.random.randn(200) - 1
x2 = np.random.randn(200)
x3 = np.random.randn(200) + 1

hist_data = [x1, x2, x3]

group_labels = ['Group 1', 'Group 2', 'Group 3']
colors = ['#333F44', '#37AA9C', '#94F3E4']

# Create distplot with curve_type set to 'normal'
fig = ff.create_distplot(hist_data, group_labels, show_hist=False, show_rug=False, colors=colors)

# Add title
fig.update_layout(title_text='Curve and Rug Plot')
fig.show()