dev : Add email body generation factory class

Author: LeeJeongGi

bm-controller/src/main/java/org/benchmarker/bmcontroller/mail/common/factory/EmailBodyGenerator.java

@@ -0,0 +1,6 @@
+package org.benchmarker.bmcontroller.mail.common.factory;
+
+public interface EmailBodyGenerator {
+
+    String createBody(String... args);
+}

bm-controller/src/main/java/org/benchmarker/bmcontroller/mail/common/factory/EmailVerificationFactory.java

@@ -0,0 +1,12 @@
+package org.benchmarker.bmcontroller.mail.common.factory;
+
+public class EmailVerificationFactory implements EmailBodyGenerator {
+
+    @Override
+    public String createBody(String... args) {
+
+        String authNum = args[0];
+
+        return "안녕하세요!\n\n, 회원 가입을 위한 인증 코드를 안내드립니다. 아래의 인증 코드를 입력하여 계정을 활성화하세요:\n\n인증 코드: " + authNum;
+    }
+}