fix: 邮件标题自定义

wfc-common/wfc-common-mail/src/main/java/org/wfc/common/mail/config/properties/MailProperties.java

@@ -66,4 +66,9 @@ public class MailProperties {
      * Socket连接超时值，单位毫秒，缺省值不超时
      */
     private Long connectionTimeout;
+
+    /**
+     * 邮件标题
+     */
+    private String subject;
 }