Support Elasticsearch meta fields

[dai-chen]

Support Elasticsearch meta fields, ex. _id, _index etc.

[dai-chen]

There are options like SELECT _id or ID() or META('_id') etc. Need to evaluate pros and cons for each.

[nagakrishna]

OpenSearch's Query bench with SQL support is a great. For our customers (works with SQL), who queries and manipulates data, we are investigating to use open search to store data. As OpenSearch's SQL plugin doesn't supports UPDATE statement #541, we were checking on other potential options to leverage the same. One option is to use meta fields like _id and then use DSL to update the data. Having this feature implemented would benefit us.