Maven examples & Gradle update

[hankem]

This PR

• adds pom.xml files to run the examples with Maven
• updates Gradle to support more modern Java versions
• improves the user experience when running the junit5 examples with IntelliJ IDEA

[hankem]

FYI: TNG/ArchUnit#1450 will update these pom.xmls with every release of ArchUnit.

[codecholeric]

I appreciate the initiative to also make these examples work with Maven, but do you think it's easy to understand if both Maven and Gradle are mixed together? Or should we have dedicated examples? 🤔 In the end we're updating those automatically anyway, right? We could also adapt that to generate two sets of examples, one for Gradle and one for Maven?

Also, would it make sense to use the https://maven.apache.org/wrapper/ analogously to Gradle?

[hankem]

do you think it's easy to understand if both Maven and Gradle are mixed together? Or should we have dedicated examples?

As this repository is about ArchUnit examples, I thought it would be fair to support multiple build tools in the same module (and not duplicate the examples just because there are several ways to run them). Would it be more clear to state in the README:

You can run them

• with Gradle (using the provided build.gradle scripts):

  ./gradlew test
  

• with Maven (using the provided pom.xml files in the same directories):

  ./mvnw test
  

• or directly from your IDE.

[hankem]

would it make sense to use the https://maven.apache.org/wrapper/

Good idea!