[ResponseOps] Elasticsearch Query rule: handle is_partial in ES|QL queries

[pmuellr]

From https://elasticco.atlassian.net/browse/ES-8808, ES|QL results will start coming back with an is_partial flag set, if for some reason the query could not be completed but there are some results. The information about skipped clusters will come back in the _clusters metadata property.

My guess is, that because the info is coming back in the _clusters metadata, we're already handling it with the code we merged here: PR #189312

We should check to see if this is true (wonder how we can check?). We may want to also actually check the is_partial field explicitly here, as it sounds like it may be used in the future in other cases.

If this works with the existing code, the rule would process the returned (partial) results but generate a warning. I assume that behavior is still what we want ...

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)