Allow copy the source code of an aggregation in search/dashboards

[todvora]

What?

Sometimes I am using the search/dashboard UI as a "builder" to generate an aggregation request, that will be then used for scripting purposes via the Search REST endpoint. It would be really helpful to provide a "copy aggregation source code" item in the actions menu.

Why?

To assist users when they want to use aggregations via API calls.