[FEATURE] Support flat object querying and searching

[Yury-Fridlyand]

Is your feature request related to a problem? Support new OpenSearch data type: flat_object

What solution would you like?

1. Support querying such fields, for example in select * query.
2. Support search for sub-fields of such fields.

What alternatives have you considered? N/A

Do you have any additional context? https://opensearch.org/docs/latest/field-types/flat-object https://github.com/opensearch-project/OpenSearch/pull/6507

[kedbirhan]

this issues have been open for a year now anyone going work on this???.