add missing timezone parameter in nuxeo-aggregate-data-behavior

As of today this elements only returns date histogram based on UTC time.

The consequence is that the histogram does not display correct values in the user timezone.

Example:
A document is created on April 1st at 8am in Japan. Japan time UTC+9 so the document will be counted in the March 31st bucket in the aggregate.

The date histogram aggregate has a timezone parameter to solve this problem
https://www.elastic.co/guide/en/elasticsearch/reference/6.5/search-aggregations-bucket-datehistogram-aggregation.html

the timezone parameter can be initialized this way to use the client timezone

timezone: {
  type: String,
  value: function() {
     return moment().format("Z");
  }
}

and then added to the object initialized at this line:
https://github.com/nuxeo/nuxeo-dataviz-elements/blob/e2394040cf000e151cd5af9c3b032c1141ee16d0/nuxeo-aggregate-data-behavior.html#L215

This issue can be seen in the default dashboards in Webui.