appstreamutils: suspend componentsByCategoriesTask for a bit

this should improve UI responsiveness while loading all apps, at the cost of loading the apps slower. the problem here is that as we basicaly enumerate all components known to appstream we have a substantial amount of work to run through. this takes a noticable amount of time even on fast systems. during this time the UI is effectively frozen.

to resolve this problem the function is now a coroutine and suspends itself for a bit of time so the eventloop has time to process inputs and redraw itself.