Add fleet health status reporting

Update cloudbeat to report its health status, providing better visibility into the operational state for users.

Cloudbeat should report its health status using the [`context.UpdateStatus()`](https://github.com/elastic/beats/blob/9190f776f5fb612a880cb013a9eec8a49fe17afd/filebeat/input/v2/input.go#L112) method. Status changes should only be reported when the status actually changes (don't repeatedly send HEALTHY if the status is already HEALTHY).

### Status Reporting
Cloudbeat should report the following states:

- **STARTING**: TBD
- **CONFIGURING**: TBD
- **HEALTHY**: TBD
- **DEGRADED**: TBD
- **FAILED**: TBD

Include relevant context information with non-HEALTHY states:

- TBD

## References
See the CEL input implementation for reference:
https://github.com/elastic/beats/blob/6409d005a31e0147a40f0872794880b3df15a69c/x-pack/filebeat/input/cel/input.go#L111