[FEATURE] Support search for fields in text

[Yury-Fridlyand]

Is your feature request related to a problem?

sql/opensearch/src/main/java/org/opensearch/sql/opensearch/storage/script/filter/lucene/LuceneQuery.java

Lines 227 to 240 in 34be98d

	/**
	* Convert multi-field text field name to its inner keyword field. The limitation and assumption
	* is that the keyword field name is always "keyword" which is true by default.
	*
	* @param fieldName field name
	* @param fieldType field type
	* @return keyword field name for multi-field, otherwise original field name returned
	*/
	protected String convertTextToKeyword(String fieldName, ExprType fieldType) {
	if (fieldType == OPENSEARCH_TEXT_KEYWORD) {
	return fieldName + ".keyword";
	}
	return fieldName;
	}

sql/opensearch/src/main/java/org/opensearch/sql/opensearch/storage/script/ScriptUtils.java

Lines 20 to 29 in 34be98d

	/**
	* Text field doesn't have doc value (exception thrown even when you call "get")
	* Limitation: assume inner field name is always "keyword".
	*/
	public static String convertTextToKeyword(String fieldName, ExprType fieldType) {
	if (fieldType == OPENSEARCH_TEXT_KEYWORD) {
	return fieldName + ".keyword";
	}
	return fieldName;
	}

1. convertTextToKeyword is not used everywhere (e.g. relevance search functions);
2. fields property could has any name;
3. There are 2 duplicate functions.

{
  "mappings": {
    "properties": {
      "motto": {
        "type": "text",
        "fields": {
          "words": {
            "type": "keyword",
            "ignore_above": 256
          }
        }
      }
    }
  }
}

What solution would you like?

Use mapping info to properly set fields name - words in the given sample.

What alternatives have you considered?

Add limitation section to documentation and return error on querying such kind of fields (aka columns).

Do you have any additional context?

Related to #794, #1038 and #1112.