fix(monitoring): register DtlsConfig and build DTLS config from Californium standard defaults

new Configuration() started from an empty config with only SystemConfig/CoapConfig
registered, leaving DTLS module defaults unset. Register DtlsConfig and build from
Configuration.getStandard() so unset DTLS properties fall back to Californium's
own defaults instead of remaining unspecified.

monitoring/src/main/java/org/thingsboard/monitoring/service/transport/impl/CoapTransportHealthChecker.java

@@ -23,6 +23,7 @@ import org.eclipse.californium.core.coap.MediaTypeRegistry;
 import org.eclipse.californium.core.config.CoapConfig;
 import org.eclipse.californium.core.network.CoapEndpoint;
 import org.eclipse.californium.elements.config.SystemConfig;
+import org.eclipse.californium.scandium.config.DtlsConfig;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 import org.springframework.context.annotation.Scope;
 import org.springframework.stereotype.Component;
@@ -42,6 +43,7 @@ public class CoapTransportHealthChecker extends TransportHealthChecker<CoapTrans
     static {
         SystemConfig.register();
         CoapConfig.register();
+        DtlsConfig.register();
     }
 
     private CoapClient coapClient;

monitoring/src/main/java/org/thingsboard/monitoring/util/DtlsClientConnectorFactory.java

@@ -64,13 +64,14 @@ public class DtlsClientConnectorFactory {
     static {
         SystemConfig.register();
         CoapConfig.register();
+        DtlsConfig.register();
     }
 
     private DtlsClientConnectorFactory() {
     }
 
     public static DTLSConnector jvmTrustedDtlsClientConnector() {
-        Configuration config = new Configuration();
+        Configuration config = Configuration.getStandard();
         config.set(DtlsConfig.DTLS_ROLE, DtlsConfig.DtlsRole.CLIENT_ONLY); // no client cert required
         config.set(DtlsConfig.DTLS_USE_SERVER_NAME_INDICATION, true); // select the correct server cert
         config.set(DtlsConfig.DTLS_SIGNATURE_AND_HASH_ALGORITHMS, CLIENT_SIG_ALGS);