Trigger post-update events for Package updates.

[isoos]

• Single and explicit method call for all potential post-update events.
• Cache is always purged, task update and API export can be skipped.
• API export partial skip is indicated with a new flag (skipVersionsExport), but it is not implemented yet.
• Updated all but one uses of purgePackageCache (TBD later if/how that should be changed).
• The trigger method and also the AsyncQueue update returns an optional Future that can be awaited, but doesn't cause linter issues when not awaited.
• If we like this pattern, I would also implement it for the other entities too.