Show new version available message on dashboard when plugin/octopi update is available

[martijnvankekem]

Is your feature request related to a problem? Please describe. With OctoDash and the link in PrusaSlicer, I hardly have to open the web dashboard anymore, hence I'm missing some available updates.

Describe the solution you'd like It would be nice if a small notification would popup on OctoDash when a new update is available for any installed plugin or OctoPi itself.