UX for different StartupTaskState

I feel like for this (and the other StartupTaskState) we should display a warning of some sort. But I'd be ok with just ignoring these cases for now and linking a new GitHub issue for a separate PR.

Originally posted by @carlos-zamora in https://github.com/microsoft/terminal/pull/4908

Additional context:

Specifically, StartupTaskState::DisabledByUser is the primary case to handle. The value of displaying feedback to users for the other states could be debated; I'm not aware of other applications that pop a dialog or feedback when the "start application on windows start" checkbox or whatnot is changed, but those applications generally don't have users managing settings via Notepad :)