Update Spring Boot release, adding Gradle build and cleanup

- Update Spring Boot release, Checkstyle, Mysql.
- Formatting pom.xml with sortpom-maven-plugin.
- Rename README to standard file name.
- Adding GitHub Action for Gradle.

.github/workflows/maven-build.yml

@@ -1,5 +1,5 @@
 # This workflow will build a Java project with Maven, and cache/restore any dependencies to improve the workflow execution time
-# For more information see: https://help.github.com/actions/language-and-framework-guides/building-and-testing-java-with-maven
+# For more information see: https://docs.github.com/en/actions/use-cases-and-examples/building-and-testing/building-and-testing-java-with-maven
 
 name: Java CI with Maven
 
@@ -26,4 +26,4 @@ jobs:
           distribution: 'adopt'
           cache: maven
       - name: Build with Maven Wrapper
-        run: ./mvnw -B package
+        run: ./mvnw -B verify