Feature Request: Support for SNR/SNA and PNR/PNA on Sh interface

[Kumarsatyam1]

When an Application Server (AS) sends a Subscribe-Notifications-Request (SNR, Command Code 308) to subscribe to changes in the subscriber profile, PyHSS drops the packet because it lacks the corresponding Answer_16777217_308 function.

Additionally, PyHSS does not have the logic to act as a client to send a Push-Notification-Request (PNR, Command Code 309) to the AS when the user data is actually modified.

Expected Behavior for both:

1. SNR/SNA: PyHSS should parse the Subscribe-Notifications-Request, store the AS subscription details (Subs-Req-Type, Data-Reference) in the database, and return a Subscribe-Notifications-Answer (SNA) with Result-Code: 2001.

2. PNR/PNA: When the subscribed data is updated in the HSS (e.g., via web UI or API), PyHSS should actively construct and send a Push-Notification-Request (PNR) to the subscribed AS, and wait for a Push-Notification-Answer (PNA) acknowledgment.

It would be really helpful if the notification capabilities (SNR/PNR) could be added to complete the Sh interface feature set.