Feature Request: Option to disable notifications on periodic syncs

[kitschpatrol]

The notifications popped on periodic syncs are distracting and unnecessary once trust in the plugin's basic competence has been established.

It would be nice to either remove these notifications entirely, or provide a toggle in the options to disable them.

In my opinion, this removal (or option) should only apply to automatic / periodic syncs, since direct user-initiated actions (e.g. clicking the Sync now button) should always provide positive feedback in the form of a notification.

I'm happy to provide a PR if this feature is of interest.