Poll dynamic person-card data e.g messages/reduce their cache times

[Mnickii]

          > I'd suggest just polling card messages and any other more dynamic data section; I think the invalidation period for other sections like profiles and direct reports is sufficient.

I like this idea. Can we do this as a feature on its own? It'll allow more introspection into areas we need to apply it as well as consequences around performance.

Originally posted by @musale in #3266 (comment)