[ML] Perform query field validation for rerank task type

[jonathan-buttner]

Fixes an issue where if a request did not include the task type in the URL, and the query field was not included in the request, a null pointer would be thrown.

This PR will have a validation exception be thrown indicating that the query field must be defined for the rerank task type.

Testing

Create inference endpoint

PUT _inference/rerank/jinaai-rerank
{
  "service": "jinaai",
  "service_settings": {
    "model_id": "jina-colbert-v1-en",
    "api_key": "api key"
  }
}

Issue request without task type in URL

POST _inference/jinaai-rerank
{
    "input": [
        "Carson City is the capital city of the American state of Nevada.",
        "The Commonwealth of the Northern Mariana Islands is a group of islands in the Pacific Ocean. Its capital is Saipan.",
        "Washington, D.C. (also known as simply Washington or D.C., and officially as the District of Columbia) is the capital of the United States. It is a federal district.",
        "Capitalization or capitalisation in English grammar is the use of a capital letter at the start of a word. English usage varies from capitalization in other languages."
    ],
    "return_documents": true
}

That should return with a validation error.

[elasticsearchmachine]

Hi @jonathan-buttner, I've created a changelog YAML for you.

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)

[DonalEvans]

Just a couple of minor points, not mandatory

[DonalEvans]

This is unnecessary, since the test never actually tries to get a response, as it fails in validation before sending the request.

[DonalEvans]

Nitpick, but this class uses MatcherAssert.assertThat() in a lot of places instead of using ESTestCase.assertThat() (even though they're the same under the hood). Would it improve consistency to do a quick find/replace to remove the MatcherAssert. and have all assertions using the same assertThat() method?

[jonathan-buttner]

💚 All backports created successfully

Status	Branch	Result
✅	9.2
✅	9.1
✅	8.19

Questions ?

Please refer to the Backport tool documentation