Add support for PIT API in Query watches API

[ElenaStoeva]

Description

Our team, @elastic/platform-deployment-management, is working on replacing the logic for fetching watches from Watcher in Kibana. Currently, Watcher fetches watches by searching the .watches system index, which is not recommended anymore, so we are in the process of replacing this with calls to the Query watches API instead (see elastic/kibana#152142).

We have an open PR for this where we discussed implementation details with @martijnvg. We plan to call the Query watches API using the search_after parameter, sorting on the _seq_no field. We also plan to use the Point In Time API to prevent inconsistent results across pages if a refresh occurs, but the Query watches API doesn't currently support a pit_id parameter so we are not able to utilize the PIT API. Can you please add support for it?

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[martijnvg]

The request should be able to set PointInTimeBuilder on the search request that the request of this API wraps. And the response of this API should just include the pit that the search response reports.

[ElenaStoeva]

Closing as we no longer need this - we used pagination to query the watches for the current page only - elastic/kibana#218853.