Add validation method to QueryBuilders

[cbuescher]

As part of #10669 we discussed adding the ability to validation capability to the refactored QueryBuilders. This could be a new method in the QueryBuilder interface that all queries have to implement and that can be called either after parsing (on coordinating node in the future), before or after the query gets serialized to other nodes or by hooking into the existing request validation mechanism (ActionRequest#validate).

[cbuescher]

Thoughts by @javanna: #10669 (comment)

[cbuescher]

We have a validate() in most query builders, although unused. Closing this issue.