Add #3 - properties migrator

넣어보고, 프로퍼티에 과거 로그백 설정 세팅
테스트 돌리니 안내 문구 표시되는 것 확인

```
Property source 'Config resource 'classpath:/application.properties' via location 'optional:classpath:/'':
	Key: logging.pattern.rolling-file-name
		Line: 1
		Replacement: logging.logback.rollingpolicy.file-name-pattern
```

build.gradle

@@ -1,5 +1,5 @@
 plugins {
-    id 'org.springframework.boot' version '2.5.2'
+    id 'org.springframework.boot' version '2.4.0'
     id 'io.spring.dependency-management' version '1.0.11.RELEASE'
     id 'java'
 }
@@ -13,6 +13,7 @@ repositories {
 }
 
 dependencies {
+    implementation 'org.springframework.boot:spring-boot-properties-migrator'
     implementation 'org.springframework.boot:spring-boot-starter-web'
     testImplementation 'org.springframework.boot:spring-boot-starter-test'
 }

src/main/resources/application.properties

@@ -1 +1 @@
-
+logging.pattern.rolling-file-name=rolling.txt