Add an info tooltip to dashboard plots

[jrbourbeau]

We expose many diagnostic dashboard plots to users. This is great as it provides a detailed, real-time look into a cluster's state.

However, it may not be immediately clear to users (especially new users) what information is actually being displayed in each plot. For example, users may not know that the central circle in the "cluster map" plot (a.k.a the "pew-pew plot") represents the scheduler while the surrounding circles represent workers.

One way we could better inform users would be to add an info icon ℹ️ to our dashboard plots which, when users hover their mouse over it, displays information about what the plot is displaying.

cc @charlesbluca who has been thinking about dashboard visualizations recently

[charlesbluca]

This sounds like a good idea! I think Bokeh's HelpTool should be good for this. One thing to consider is that this tool redirects to a URL on click; there are a couple options for handling that:

• Have the tool redirect to some general documentation on the dashboard
• Have the tool redirect to a specific section of the documentation explaining the plot (might be redundant)
• Make a custom tool similar to the HelpTool but with no events on click (example of a custom tool here)

[charlesbluca]

Opened up a draft of this #4759; if you get the chance, could you chime in on some of the missing descriptions there? I'm not fully familiar with all the dashboard plots myself 🙂

[ncclementi]

A bit of an update on exploring other options, to be able to have the info tooltip embedded in the plots and not as external links.
Every possible solution I have found/tried didn't work because of limitations on Bokeh. I opened an issue on Bokeh explaining what we are trying to do, the issue with feature request was added to the next Bokeh Milestone, here is the issue if you want to take a look bokeh/bokeh#11389 .