[Alerting] Track fields usage in find api

[chrisronline]

Resolves #112009

To test, you can use these sample URLs:

Legacy: https://localhost:5601/api/alerts/_find?fields=[%22hi%22]
New: https://localhost:5601/api/alerting/rules/_find?fields=[%22hi%22]

{
  "usage_counters": {
    "daily_events": [
      {
        "domain_id": "alerts",
        "counter_name": "legacyAlertingFieldsUsage",
        "counter_type": "alertingFieldsUsage",
        "last_updated_at": "2021-09-13T20:47:44.480Z",
        "from_timestamp": "2021-09-13T00:00:00Z",
        "total": 2
      },
      {
        "domain_id": "alerts",
        "counter_name": "legacyRoute_find",
        "counter_type": "legacyApiUsage",
        "last_updated_at": "2021-09-13T20:47:44.480Z",
        "from_timestamp": "2021-09-13T00:00:00Z",
        "total": 4
      },
      {
        "domain_id": "alerts",
        "counter_name": "alertingFieldsUsage",
        "counter_type": "alertingFieldsUsage",
        "last_updated_at": "2021-09-14T13:17:01.098Z",
        "from_timestamp": "2021-09-14T00:00:00Z",
        "total": 2
      }
    ]
  }
}

[elasticmachine]

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

[ymao1]

LGTM! Verified counter gets incremented when using the fields query param.

[YulNaumenko]

LGTM

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 2c0dc67
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Metrics [docs]

✅ unchanged

History

• 💚 Build #154332 succeeded d3eb432
• 💚 Build #153205 succeeded 5155434
• 💚 Build #153188 succeeded a6cbdca

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