pk: Improve when there's lots of updates

Aleix Pol Gonzalezrequested to merge
work/apol/faster-big-updates into Plasma/5.27

I opened a laptop that has KDE Neon and it had been a while and it was very stuttery and it even would overflow PackageKit the transaction limit.

  • Groups the getUpdateDetails calls into a big one, which is more efficient.
  • Stops emitting signals unnecessarily for the update resource.

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