[HLRC] Throw an exception if an http warning is returned by the server

[lipsill]

Currently the high level client silently ignores any warnings returned by the server. I stumbled on this when I deprecated a url parameter on the server side, forgot to change the high level rest client and still all client tests passed.

It is difficult to argue that any warning should result in an exception as the client does not have control over the request source provided by the user. But I think that it would be nice once a deprecated url parameter is used, the integration tests to fail (similar to the rest-api tests). What about introducing a strict testmode where any warning results in an exception? This way the used parameters and code snippets in the docs will be using always the 'correct' fields and url parameters.

I am not sure if this is something ES team is interested in pursuing. Hence this PR is intended as a starting point for a discussion rather than a solution.
(a CI run of this PR will expectedly fail as the client is currently using a deprecated endpoint)

[elasticmachine]

Pinging @elastic/es-core-infra

[jasontedor]

Awesome! We want this (see #33534), but for the low-level REST client (then we get it for both the low-level and the high-level REST client). Would you be interested in pursuing this in the low-level REST client?

[lipsill]

@jasontedor thanks for the quick feedback! I did not see that there was already an issue and a decision to proceed ;)
I will give it a shot and move the logic to the low level client.

Closing in favor of #33534

[jasontedor]

Thanks a lot @lipsill.