`plot_lm` doesn't work with `y_model` and multidimensional `y`

[colehaus]

Describe the bug When the y_model argument to plot_lm is used with multidimensional y, an exception is thrown instead of the appropriate plots being generated.

To Reproduce

See this notebook: https://gist.github.com/colehaus/b2aa195687f53ef7c86eec2ebb3798c2

Expected behavior I expected a collection of plots to be generated just like happens with plot_dim ordinarily, but there should also be the model info in the plot as happens when a single-dimensional plot is created.

Additional context Arviz version is 0.11.4.

[ayashabbar]

Hello @colehaus I would like to contribute to this issue. Are there any updated output you came across? Thanks in advance, A. Shabbar

[colehaus]

Hi, thanks for looking at it. I haven't looked into the issue at all since opening it. So the notebook is still the most up-to-date reflection of the situation.

[itsdivya1309]

Hii, has the issue been resolved? If not, I would like to work on this issue.