[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

etc/gn/openthread.gni

@@ -198,6 +198,9 @@ if (openthread_enable_core_config_args) {
     # Enable SNTP Client support
     openthread_config_sntp_client_enable = false
 
+    # Enable SRP Server support
+    openthread_config_srp_server_enable = false
+
     # Enable the time synchronization service feature
     openthread_config_time_sync_enable = false