Periodically sync dependency versions with main Jib repo

Most of the dependencies need to be sync'ed with the main Jib repo.

```build.gradle
/* PROJECT DEPENDENCY VERSIONS */
// define all common versioned dependencies here
project.ext.dependencyVersions = [
GUAVA: '28.1-jre',
JSR305: '3.0.2', // transitively pulled in by GUAVA

JIB_CORE: '0.15.0',
JIB_GRADLE: '2.4.0',

// for Build Plan and Jib Plugins Extension API
JIB_GRADLE_EXTENSION: '0.4.0',
JIB_MAVEN_EXTENSION: '0.4.0',

SPRING_BOOT: '2.3.1.RELEASE', // for Spring Boot Gradle extension
MAVEN_API: '3.5.2',

//test
JUNIT: '4.12',
MOCKITO_CORE: '3.2.4',
SLF4J_API: '1.7.25',
SYSTEM_RULES: '1.19.0',
]
/* PROJECT DEPENDENCY VERSIONS */
```