[#1#2#3] DB모델 객체 및 로그인 ,회원가입 구현

.env

+DB_HOST=localhost
+DB_USER=root
+DB_PASSWORD=0000
+DB_NAME=meeting
+MONGO_URI=mongodb://localhost:27017/your_mongo_db
+PORT=8080
+CALLBACK_URL=http://localhost:8080/auth/google/callback
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