clientlog: add NTS-KE service

Instead of sharing the NTP rate limiting with NTS-KE, specify a new
service for NTS-KE and use it in the NTS-KE server.

Add ntsratelimit directive for configuration.

test/unit/clientlog.c

@@ -36,6 +36,7 @@ test_unit(void)
     "clientloglimit 10000",
     "ratelimit interval 3 burst 4 leak 3",
     "cmdratelimit interval 3 burst 4 leak 3",
+    "ntsratelimit interval 6 burst 8 leak 3",
   };
 
   CNF_Initialise(0, 0);