[Notifications] Group similar notifications received together instead of showing them in batch

[SamuAlfageme]

Similarly as what happens when multiple files are erased at the same time and the client only displays one notification saying: "N files were deleted", when there's multiple equal events received together, they should be grouped into one notification.

Scenarios:

• When multiple folder's sync needs to be confirmed in the account tab (see Discovery: Add branding option to disable default sync of 'M' directo… #5340 (comment))