Make Inference API task_settings optional

[davidkyle]

task_settings are optional when creating an endpoint in the Inference API and may not be returned in the GET response. The spec incorrectly has task_settings as required for both creation (PUT) and retrieval (GET), this PR changes that

The Elasticsearch documentation contains an example where an endpoint is created without task_settings ,see creating the ELSER service.

[github-actions]

Following you can find the validation results for the APIs you have changed.

API	Status	Request	Response
inference.delete	⚪	Missing test	Missing test
inference.get	🟢	4/4	4/4
inference.inference	⚪	Missing test	Missing test
inference.put	⚪	Missing test	Missing test
inference.stream_inference	🟠	Missing type	Missing type

You can validate these APIs yourself by using the make validate target.

[pquentin]

Thanks! This pull request makes a response field optional, which is why I asked a review from static client maintainers here.

[l-trotta]

no problems for java

[pquentin]

After discussion with the team, the conclusion is that making a response field optional is OK. User code handling the case where task_settings is set won't change. (Except in Rust, where it won't compile because the value will be wrapped in std::Option. But the Rust client isn't ready yet.)

Making a field optional in requests is actually more of an issue, because that means constructors need to change to include a variant without that field. Before that change, users will be forced to set this field.

But in any case, since this a bug fix to a tech preview API, this pull request is fine. I would guess that today multiple clients would be failing if given a payload without task settings anyway.