text: Title: AlertClient.find returns an incorrect Type when the `fields` options is used
  Body: the `find` api claims to return `SanitizedAlert` types, but this is not true when the `field` options is used to narrow down the returned fields.
  
  We should address as it could cause mistakes in `getAlertFromRaw` which could in theory break `find` when `fields` is used.
  At the moment we're only aware of a use of `fields` in siem, but we don't know who might rely on this in their own implementations in the future.
  
  This can be cleaned up when telemetry from https://github.com/elastic/kibana/issues/108716 shows usage is below 1% or deprecated for > 2.5 years after deprecating legacy terminology usage.