ThrowExceptions xmldocs is misleading

[octocat-mona]

NEST/Elasticsearch.Net version:
6.3.1

Elasticsearch version:
6.5.0

Description of the problem including expected versus actual behavior:
Apparently it was decided to not always throw in case IsValid is false (see #2153, #2385).
My issue is not to reconsider this (although it would be nice to have this functionality somehow) but rather to clarify the documentation of ThrowExceptions which states:

...always throw an exception on the client when a call resulted in an exception on either the client or the Elasticsearch server.

Because I assumed I do not have to check a response for IsValid to be false I actually introduced a bug in my code. Maybe the xmldocs can be updated to state that always is not always always? 😉

Steps to reproduce:

1. Create new ElasticClient instance using ConnectionSettings.ThrowExceptions()
2. Call a method like UpdateByQuery which causes an error (like a document object not passing the strict mapping validation)
3. No exception is thrown

[Mpdreamz]

@KPStolk this would be a a great first PR ;)

[octocat-mona]

@Mpdreamz Will look into it soon 😄

[octocat-mona]

@Mpdreamz Created PR #3518 , I hope this is a simple and accurate description?

[Mpdreamz]

PR is merged 🎈