[Change Proposal] Provide human-readable name to integration inputs

Proposal coming from the discussion in https://github.com/elastic/kibana/issues/132263

Creating an integration (package-policy) with Fleet API requires specifying input types, and its meaning is not obvious for users.

Could we extend package-spec with a new field in inputs, that would be a human-readable value?
This would make it easier for users to create integrations.

Current API:
```
POST http://elastic:changeme@localhost:5601/julia/api/fleet/package_policies
kbn-xsrf: kibana

{
"name":"apache-5",
"inputs": [
{"type":"logfile","enabled":true},
{"type":"apache/metrics","enabled":false}
],
"package": {
"name":"apache",
"version":"0.3.3"
}
}
```

Proposed change:
```
"inputs": [
{"id":"apache_logs","enabled":true},
{"id":"apache_metrics","enabled":false}
],
```

The proposed change would require updating all packages' inputs with unique id values.

cc @joshdover