[FEATURE]: Show baseline image in test dashboard

[my-tien]

It would be useful if the test dashboard also showed the baseline image below the freshly generated figure. That way one can quickly compare to the reference and find potential bugs quicker. Here is how it could look like: A button below the generated figure for toggling the baseline image:

[my-tien]

FYI @camdecoster

[camdecoster]

What do you think of adding multiple ways of comparing the baseline to the live chart? Something similar to what GH does with image diffing in PRs? Also, it's important to keep in mind that the images won't necessarily match since the baseline is generated using Kaleido and the live version in your browser.

[my-tien]

That part about Kaleido is a good point. Maybe it's smarter to show the rendering of a previous version by pulling it in via https://cdn.plot.ly (and have some logic to switch between the working tree and that version for rendering the two figures).
There could be an input field to specify the desired old plotly version too.

Then there would be no image diffing of course.