Ability to attach arbitrary params/notes to scalars tooltip

[LukeAI]

If I run a bunch of experiments and look back on the curves, I often can't remember all the tweaks that I've made. It'd be really nice if I could attach the hyperparameters and maybe even notes to the hovertext so that I can see at a glance what the differences between the different curves are

eg.

related my SO question on this: https://stackoverflow.com/questions/66109908/how-to-attach-list-of-constants-to-a-run-in-tensorboard?noredirect=1#comment116886040_66109908