MM-13190: Fix NotifyProps in Bulk Import. (#9900)

If some, but not all, notify props are specified for a user in the bulk
import data, and that is a newly created user, we must explicitly
initialise all the other notify props to their default values to avoid
breaking client assumptions.

app/import_functions.go

@@ -279,6 +279,7 @@ func (a *App) ImportUser(data *UserImportData, dryRun bool) *model.AppError {
 	} else {
 		user = &model.User{}
 		user.MakeNonNil()
+		user.SetDefaultNotifications()
 		hasUserChanged = true
 	}