Onboard Error Count Threshold rule type with FAAD

[doakalexi]

Towards: #169867

This PR onboards the Error Count Threshold rule type with FAAD.

To verify

1. Run the following script to generate APM data:

node scripts/synthtrace many_errors.ts --local --live

2. Create an error count threshold rule.
   Example:

POST kbn:/api/alerting/rule
{
  "params": {
    "threshold": 25,
    "windowSize": 5,
    "windowUnit": "m",
    "environment": "ENVIRONMENT_ALL"
  },
  "consumer": "alerts",
  "schedule": {
    "interval": "1m"
  },
  "tags": [],
  "name": "testinggg",
  "rule_type_id": "apm.error_rate",
  "notify_when": "onActionGroupChange",
  "actions": []
}

3. Your rule should create an alert and should saved it in .internal.alerts-observability.apm.alerts-default-000001
   Example:

GET .internal.alerts-*/_search

4. Recover the alert by setting threshold: 10000

5. The alert should be recovered and the AAD in the above index should be updated kibana.alert.status: recovered.

[doakalexi]

/ci

[elasticmachine]

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

[cauemarcondes]

LGTM

[elasticmachine]

Pinging @elastic/obs-ux-infra_services-team (Team:obs-ux-infra_services)

[js-jankisalvi]

Works as expected 👍

[pmuellr]

LGTM!

I really love this test section you've kinda standardized - generate data, create rule with DevTools, etc. Nice!

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 7a900f0

Metrics [docs]

✅ unchanged

History

• 💚 Build #198977 succeeded 1f92577

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @doakalexi