[Event log][7.x] Update event log client to search across legacy IDs

[chrisronline]

Relates to #100067
Blocked by #56771

In #108075, we are adding a new field to every rule saved object that points to the legacy ID (which is the current ID in 7.x but will potentially differ from the ID in 8.0). To support this new field, we need to change the event log client to accept this new ID field and use it in the query to ensure we find all relevant logs.

There is a chance that we will encounter a conflict scenario, where a legacy ID matches some migrated ID. In this case, we need to rely on this change which will add the version to the event log and handle that in our query appropriately.

See the PoC PR for more insight into how this might work.

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[mikecote]

@chrisronline Regarding the scope of this issue, is it a separate issue to make findEventsBySavedObjectIds calls pass in legacyIds (ex: https://github.com/elastic/kibana/blob/master/x-pack/plugins/alerting/server/rules_client/rules_client.ts#L505), or is it part of this issue?

[chrisronline]

This should be part of the issue

[YulNaumenko]

I will add the proper changes 👍 to this PR