[PROPOSAL] Adding generic types

[RavenX86]

Bring back some sort of level of generics for search (optional use of course).
Right now after upgrading from 2 to 3 there is no way to pass an agg interface for the response anymore which causes issues for those of us that try to avoid using "as".

That being said there might also be the options to add an extra type property for each aggregate, though most likely this is not possible due to trying to automatically generate the js SDK from the API specification. The Common_Aggregations aggregate union does not allow in any simple way to differentiate between its members.

That being said, and I know this was mentioned before, some up-to-date TS examples would be very helpful.

[nhtruong]

The use of generic was troublesome (hard to account for as an edge case for code generator, and it's not playing nice with IDEs). We discussed this topic at length here. Basically we traded it for thousands of types generated from the Spec. We definitely want to bring generic back when we have a proper solution for it.