Refactor alerting task runner - remove RecoveryActionGroupId

[doakalexi]

Meta issue: #124206

While Ersin was working on the alerts summary POC he realized that having a separate RecoveryActionGroupId is making refactoring hard. It is forcing us to do tons of type conversion tricks. Can't we get rid of it? it's just another ActionGroupId, why do we separate it?

[mikecote]

I found a place using a custom recovery action group. It's within the geo threshold rule type => https://github.com/elastic/kibana/blob/main/x-pack/plugins/stack_alerts/server/rule_types/geo_containment/alert_type.ts#L233-L238 so we'll have to keep that in mind if we remove it.