[Discover] Create executor for alerting MVP

[lukeelmers]

Blocked by #71096 and #61313

As part of the MVP for alerting in Discover, we'll need the alert creation UI to register an executor with the alerting service.

At a minimum, the executor would need to capture the following:

• Target index for query
• ES DSL that represents the query/filter/timerange of the current view. The search service will provide a way to get the necessary DSL ([data.search] Expose utility for converting a query to ES DSL #71096).
• Link back to the Discover app with query string params filtered to this view

Most of this work will probably happen in the Discover app itself, but tagging @elastic/kibana-app-arch here in case there are ways we will need to support this effort.

[lukeelmers]

pinging @elastic/kibana-app (since somehow elasticmachine did not)

[timroes]

Closing in favor of #117532