Migrate Term Aggregate max returned bucket value + update help label following elasticsearch 5.x upgrade

https://github.com/nuxeo/nuxeo-studio/blob/master/nuxeo-studio-ui/src/main/java/com/nuxeo/studio/client/help/HelpConstants.java#L267 pointing to https://github.com/nuxeo/nuxeo-studio/blob/master/nuxeo-studio-ui/src/main/resources/OSGI-INF/help.properties#L1287 which says:

Set to 0 to get all the buckets. This is mandatory when the terms aggregate \
is rendered as a select widget.

which is not true anymore for es 5.x (TP 9.3). See https://www.elastic.co/guide/en/elasticsearch/reference/2.4/search-aggregations-bucket-terms-aggregation.html

Deprecated in 2.4.0.
The ability to set size to 0, resulting in the size being set to Integer.MAX_VALUE, is deprecated, and will be removed in the next major release.

Moreover a size set to 0 will produce an error becaue es will throw an error saying it can't parse the query. Not sure if Studio should display an error if value is 0 or if the platform should translate 0 to Integer.MAX_VALUE while generating the es query.

TODO
For TP 9.3+

• Replace current help label with:

Define a positive number for the maximum number of terms to be displayed (a bucket = a term). Note that a high value can have impacts on performances, therefore we recommend to set it to a few tens at most. When using [Elasticsearch 2.4 or less](https://www.elastic.co/guide/en/elasticsearch/reference/2.4/search-aggregations-bucket-terms-aggregation.html#_size in a new page) (compatible with Nuxeo Server prior to 9.3), setting a value of 0 will return all buckets.

• Add a validation warning when value is set to 0

Setting number of buckets to 0 is not recommended since this option has been [removed in Elasticsearch](https://www.elastic.co/guide/en/elasticsearch/reference/2.4/search-aggregations-bucket-terms-aggregation.html#_size). Nuxeo Server will automatically use a value of 1000 instead to prevent errors, but this might affect your performances.