Add support for configuring WSS4J's USE_SINGLE_CERTIFICATE option

This commit allows to configure the `USE_SINGLE_CERTIFICATE` option,
which enables the choice of using valueType X509PKIPathv1 instead of
X509v3.

See gh-153

spring-ws-security/src/main/java/org/springframework/ws/soap/security/wss4j2/Wss4jSecurityInterceptor.java

@@ -595,6 +595,14 @@ public class Wss4jSecurityInterceptor extends AbstractWsSecurityInterceptor impl
 		this.enableRevocation = enableRevocation;
 	}
 
+	/**
+	 * Enables the {@code useSingleCertificate} attribute on WS-Security headers on outgoing messages. Default is
+	 * {@code true}.
+	 */
+	public void setUseSingleCertificate(boolean useSingleCertificate) {
+		handler.setOption(WSHandlerConstants.USE_SINGLE_CERTIFICATE, useSingleCertificate);
+	}
+
 	/**
 	 * Set the WS-I Basic Security Profile compliance mode. Default is {@code true}.
 	 */