[FEATURE] Boost functionality support for MultiMatchQuery

We are porting from ES 6.X to OS 2.X. In the old org.elasticsearch.index.query.MultiMatchQueryBuilder there is a field method which accepts field name and the boost value. So each field can be boosted as desired. But with the new org.opensearch.client.opensearch._types.query_dsl.MultiMatchQuery.Builder we don't have a method like this. So we can't set boost values.

I believe having same old field method is required to set the boost values for each field. See below the old method code

    if (Strings.isEmpty(field)) {
      throw new IllegalArgumentException("supplied field is null or empty.");
    } else {
      this.fieldsBoosts.put(field, boost);
      return this;
    }
  }

Although I didn't see any documentation about it but I suspect setting boost values on a field can be achieved via updating the field name. So boost a field named "title" we can add field like this. Even we have this feature should we also have a method for field boost? I think we should.
multiMatchQueryBuilder.fields("title^10")

Start by locating the org.opensearch.client.opensearch._types.query_dsl.MultiMatchQuery.Builder and compare its field handling with the old org.elasticsearch MultiMatchQueryBuilder.field(String, float) method shown here. Check whether fields("title^10") already provides equivalent behavior; done means the supported approach for per-field boost values is clear and, if needed, the builder exposes the requested capability.