Support one call-status subscription per registration (drop mandatory sessionId)

[deepakjaiswal1]

Problem description

The current design forces a call-status subscription (org.camaraproject.webrtc-events.v0.session-status) to include sessionId, meaning the client must create a new subscription for every call instance.

• Unknown before the fact – Whether the call is outgoing or incoming, the client does not know the sessionId until after it receives the POST response (outgoing) or session-invitation event (incoming).
• Race window – Establishing the subscription after the ID is learned allows status events to be published before the new subscription is active, causing missed notifications.
• Unnecessary churn – Spawning and deleting subscriptions for every call adds load to both client and gateway with no functional benefit.

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Expected behavior

• Make sessionId optional in subscriptionDetail.
• When sessionId is omitted, the subscription applies to all sessions associated with the supplied registrationId, covering both outgoing and incoming calls from the first status event onward.
• If a client still needs to scope to a single call, it may include sessionId; otherwise, the per-registration subscription is the recommended default to eliminate race conditions and event loss.

[stroncoso-quobis]

LGTM