[Filebeat] Add health status reporting to syslog input

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

The syslog input 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
The input 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

Start with filebeat/input/v2/input.go and compare the CEL input implementation at x-pack/filebeat/input/cel/input.go. Trace the syslog input's lifecycle and determine the intended meanings and context for each listed status. Done means reporting status transitions through context.UpdateStatus() without repeating unchanged states, but the TBD requirements need clarification first.

Written by the indexing model from the issue text.