[FEATURE] Support Boosting for Neural Query

[yudhiesh]

Is your feature request related to a problem?

A clear and concise description of what the problem is, e.g. I'm always frustrated when [...].
Currently, when using semantic search I have an issue where it perform poorly over exact keyword search with boosting for situations where I would like to artificially boost certain indices due to businees goals.

Sample Output:

{
  "took": 29,
  "timed_out": false,
  "_shards": {
    "total": 2,
    "successful": 2,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 28,
      "relation": "eq"
    },
    "max_score": 0.66891545,
    "hits": [
      {
        "_index": "A",
        "_id": "A-hjHkg4JVoxyrjVaY1T1fC",
        "_score": 0.66891545,
      },
      {
        "_index": "A",
        "_id": "A-4IIkZsGqs6AAGNJBPxFG2q",
        "_score": 0.66891545,
      },
      {
        "_index": "A",
        "_id": "A-PrFcKYXMGHTF6DSZ15zxw",
        "_score": 0.6600258,
      },
      {
        "_index": "B",
        "_id": "B-ppZ_YYBf08C9I8emn4W",
        "_score": 0.6593717,
      },
      {
        "_index": "A",
        "_id": "A-55mffVK1TqNteVpb6mri5d",
        "_score": 0.659091,
      }
    ]
  }
}

In this scenario I would like to apply a constant boost of 0.1 to the _score of index B .
I tried doing it within the Java Client like so:

NeuralQuery neuralQuery = new NeuralQuery.Builder()
                    .field(...)
                    .queryText(...)
                    .modelId(MODEL_ID)
                    .k(KNN_TOP_K)
                    .build();
            Query query = new Query.Builder()
                    .neural(neuralQuery)
                    .build();
            List<Map<String, Double>> indicesToBoost = List.of(Map.of(
                    "B", 0.1
            ));

            var searchResponse = openSearchJavaClient.search(
                    s -> s.index(UniversalSearchCategory.SEMANTIC_OFFERS.getIndexName())
                            .from(param.getOffset())
                            .size(param.getLimit())
                            .sort(sortOptions)
                            .query(query)
                            .source(sourceConfig)
                            .indicesBoost(indicesToBoost)
                    , Object.class
            );

But the scores do not get boosted at all.

What solution would you like?

A clear and concise description of what you want to happen.
I would like to see the score of the index B increase by 0.1.

{
        "_index": "B",
        "_id": "B-ppZ_YYBf08C9I8emn4W",
        "_score": 0.7593717,
}

What alternatives have you considered?

A clear and concise description of any alternative solutions or features you've considered.

Do you have any additional context?

Add any other context or screenshots about the feature request here.

[yudhiesh]

Just to add I am also querying an alias but trying to boost a specific index within the alias.