Extract sync tasks (and command traits) to separate package

[daften]

E.g. protected function syncTask(), public function digipolisSyncLocal()

New package name robo-digipolis-sync

[Jelle-S]

Might be more work than I anticipated initially.

Both the sync and the deploy tasks use the backup tasks, which means we'd have to create an additional package for the backup tasks.

Also the backup, sync and deploy tasks all depend on the getRemoteSettings method, which means we'd have to extract that as well. Although consolidation/robo#552 might be a big help here...

[daften]

Let's at least wait until that PR is merged, and see what refactors might follow after that.

[greg-1-anderson]

n.b. consolidation/robo#552 now supports injecting default values for task setter methods from configuration. You should review that PR and the associated documentation it contains to see if it meets your use-case for configuration.