[FEATURE] Support keyword and text data types for PPL

[Yury-Fridlyand]

Is your feature request related to a problem?

PPL returns string for all string data, which is actually incorrect. It is subject to change, see opensearch-project/sql#1296.

What solution would you like?

Observability should support and distinguish keyword and text types both.

What alternatives have you considered?

N/A

Do you have any additional context?

Under the hood keyword and text could be processed as regular strings, but the end user should be able to see the real types.

Maybe it is supported already, so you can close this ticket.

[Yury-Fridlyand]

As a member of SQL plugin team I'm happy to provide a private build of the SQL plugin which returns keyword and text instead of string.