[Meta] Enhance input Health reporting from agent to better convey issues related to installation of `unprivileged` agent

[nimarezainia]

• Depends on https://github.com/elastic/elastic-agent/issues/4683 (see related comment: https://github.com/elastic/beats/issues/39604#issuecomment-2115622565)

If the agent is provisioned in the unprivileged mode there may be data sources which won't be readable by the agent, as they require higher privilege to be accessed. This will cause the agent to go into a degraded state and show the integration as unhealthy.

Since the agent knows that it is running in an unprivileged mode AND can recognize that there's an issue with reading the input, it would be great to have this information propagated back to Fleet. Ideally the user has enough information to know that their input is unhealthy due to the fact that agent is in unprivileged mode.

Filebeat health reporting implementation: https://github.com/elastic/beats/pull/39209

- [ ] https://github.com/elastic/beats/issues/39733
- [ ] https://github.com/elastic/beats/issues/39734
- [ ] https://github.com/elastic/beats/issues/39735
- [ ] https://github.com/elastic/beats/issues/39736
- [ ] https://github.com/elastic/beats/issues/39737