[FEATURE] Support bucket size for MultiTermAggregation

[fabiankopatschek]

Is your feature request related to a problem?

Using the MultiTermAggregation returns the default bucket size of 10. By setting the size parameter (see Bucket aggregations), you could get more buckets. In this library the possibilty is missing to set the "size" parameter. The MultiTermAggregation Object has only the "terms" attribute.

What solution would you like?

Add the missing attribute to the MultiTermsAggregation type.

What alternatives have you considered?

An alternative could be using any HttpClient library instead.

Do you have any additional context?

In this forum post the issue was also addressed by someone else: No Support to change the default bucket value in MultiTermAggregation

In all the type classes is the hint, that it is generated code. But i could not find any documentation on how or where to set the attribute and generate the type classes. Maybe then i would have done a Pull Request instead of this Feature Request.

[wbeckler]

This sounds like a good idea. Feel free to propose an interface, or even better, a test case that would illustrate the correct approach.

[fabiankopatschek]

I added the code in my fork. The forked version is used in our production system.
I created a pull request for the changes.
I noticed that the "generated code comment" is no longer applicable #598
I couldn't find any exclusive testcases for this model classes, so there is no new testcase.

[VachaShah]

Done via #627