[net] SRP server implementation (#5986)

This PR includes the initial implementation of the SRP server
defined in https://tools.ietf.org/html/draft-ietf-dnssd-srp-07.

- SRP server Service TLV propagation: Includes only the 2-bytes
  dynamic listening port in the Server TLV.
- SRP request processing (parsing & validation)
- LEASE & KEY-LEASE management
- SIG(0) verification
- Interface for advertising proxy
- CLI commands for testing
- Support removing indivitual SRP service

src/core/common/notifier.cpp

@@ -183,6 +183,9 @@ void Notifier::EmitEvents(void)
 #if OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE
     Get<BorderRouter::RoutingManager>().HandleNotifierEvents(events);
 #endif
+#if OPENTHREAD_CONFIG_SRP_SERVER_ENABLE
+    Get<Srp::Server>().HandleNotifierEvents(events);
+#endif
 #if OPENTHREAD_CONFIG_SRP_CLIENT_ENABLE
     Get<Srp::Client>().HandleNotifierEvents(events);
 #endif