… field (elastic#204410)

## Summary

Closes elastic#203821

Added a function to Fleet setup to query package policies that are
missing `supports_agentless` field and backfilling them. Only doing this
for `cloud_security_posture` package, to skip other non-related packages
like `system`.

To verify:
- follow the steps in the description here to create an agentless agent
policy with cspm integration:
elastic#199567
- manually update the package policy to simulate
`supports_agentless:false`
- trigger Fleet setup
- verify that the cspm package policy has `supports_agentless:true`

```
PUT kbn:/api/fleet/package_policies/<policy_id>
{
   "supports_agentless": false
}

POST kbn:/api/fleet/setup

GET kbn:/api/fleet/package_policies/<policy_id>
```

Logs:
```
[2024-12-16T15:42:11.027+01:00][DEBUG][plugins.fleet] Backfilling package policy supports_agentless field
[2024-12-16T15:42:11.034+01:00][DEBUG][plugins.fleet] Backfilling supports_agentless on package policies: 6a06d167-e02e-4057-9d71-e1f7e5dd2847
[2024-12-16T15:42:11.035+01:00][DEBUG][plugins.fleet] Starting update of package policy 6a06d167-e02e-4057-9d71-e1f7e5dd2847
[2024-12-16T15:42:13.213+01:00][DEBUG][plugins.fleet] Deploying policies: 0ed942d5-6c01-484f-a1c5-6c7fff92b020:12
[2024-12-16T15:42:13.610+01:00][DEBUG][plugins.fleet] Agent policy 0ed942d5-6c01-484f-a1c5-6c7fff92b020 update completed, revision: 12
[2024-12-16T15:42:13.610+01:00][DEBUG][plugins.fleet] Package policy 6a06d167-e02e-4057-9d71-e1f7e5dd2847 update completed
```

### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

(cherry picked from commit a229d7a)