Add support for SearchTemplate for reactive client

[bilak]

Hello,
it would be nice to be able to extend DefaultReactiveElasticsearchClient when it's needed to write some custom queries. For example now I'd like to implement search template however it's not that easy because of private methods sendRequest. Could we change those to protected instead of private?

Or is there any other extension point that I've missed? I'd like to use search templates.

Thanks

[sothawo]

I think we could make the three sendRequest() method protected. Although the better solution would be to add search template support by submitting a PR ;-)