[FEATURE] Add specification for paginated wlm/stats API

[saimedhi]

Is your feature request related to a problem?

• Add specification for the newly added paginated wlm/stats API.
• Related Opensearch PR : Pagination for wlm/stats api OpenSearch#17638

What solution would you like?

• Add specification

[saimedhi]

@Lindsay-00, Please consider adding specification for paginated wlm/stats API