Retrievers - Fix rank_window_size validation

[ioanatia]

When passing a negative rank_window_size to a compound retriever, we return an error message that references size instead of rank_window_size:

POST search-movies/_search
{
  "retriever": {
    "rrf": {
      "retrievers": [
        {
          "standard": {
            "query": {
              "match": {
                "title": "Shakespeare"
              }
            }
          }
        },
                {
          "standard": {
            "query": {
              "match": {
                "title": "Shakespeare"
              }
            }
          }
        }
      ],
      "rank_window_size": -1
    }
  }
}

Response:

{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "[size] parameter cannot be negative, found [-1]"
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "[size] parameter cannot be negative, found [-1]"
  },
  "status": 400
}

This is coming from:

elasticsearch/server/src/main/java/org/elasticsearch/search/builder/SearchSourceBuilder.java

Lines 517 to 519 in f0d7ec4

	if (size < 0) {
	throw new IllegalArgumentException("[size] parameter cannot be negative, found [" + size + "]");
	}

This validation needs to happen at the compound retriever level.

Besides fixing the error message, I also moved rankWindowSize to the base class for compound retrievers, instead of having it duplicated in 3 inherited retrievers.

[elasticsearchmachine]

Pinging @elastic/es-search (Team:Search)