[Response Ops][Alerting] Optimize querying for summary alerts in ExecutionHandler

[ymao1]

More details in #182181

Blocked on #186533 and #186534

Investigate optimizing getting summary queries during action scheduling so that we're not performing duplicate queries and instead caching the query results so they can be reused. If we're getting all the queries up front, we could also look into doing an msearch to perform all the queries at once.

Currently, each action is considered separately from any others and a summary query is performed for each if required. If multiple actions use the same alert filter or don't use any alert filter, we could cache the query results for reuse instead of running the same query repeatedly.

[elasticmachine]

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