fix: Initialize Prometheus healthy/recording metrics with current status

[mozkomor05]

Summary

The jitsi_jibri_healthy and jitsi_jibri_recording Prometheus gauges default to 0 and only update on status transitions via publishStatus(). Since Jibri starts healthy with no transition, the metrics remain at 0 even though the instance is healthy and idle.

This adds a single line to seed the metrics with jibriStatusManager.overallStatus immediately after registering the status handler.

Before: jitsi_jibri_healthy stays 0.0 until the first recording session triggers a state change.
After: jitsi_jibri_healthy correctly reports 1.0 from startup.

Verification

# REST API (was always correct):
curl http://localhost:2222/jibri/api/v1.0/health
# {"status":{"busyStatus":"IDLE","health":{"healthStatus":"HEALTHY","details":{}}}}

# Prometheus metric (was 0, now correctly 1):
curl -s http://localhost:2222/metrics | grep jitsi_jibri_healthy
# jitsi_jibri_healthy 1.0

Fixes #590

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.

[mozkomor05]

Done