Add `junit5-jupiter-starter-graalvm-native` sample

[sormuras]

Add minimal working example building a native "hello world" application and running Jupiter tests against it.

[marcphilipp]

I don't think we should duplicate what https://github.com/graalvm/native-build-tools/tree/master/samples/java-application-with-tests already provides.

[sbrannen]

I renamed the proposed project name to *-native since we're really showcasing native image testing support and not GraalVM as an alternative JVM.

[sbrannen]

I don't think we should duplicate what https://github.com/graalvm/native-build-tools/tree/master/samples/java-application-with-tests already provides.

Good point.

There's not much value in duplicating that.

Plus it already includes Gradle and Maven build support.

Instead of having our own example, we could just link to that one.

[marcphilipp]

Instead of having our own example, we could just link to that one.

From the readme? Or should we also include it in the user guide?

[sbrannen]

From the readme? Or should we also include it in the user guide?

Both: in the README for the junit5-samples project and in the JUnit 5 user guide.

Since we just added @DisabledInNativeImage support (which links to the NBT project), I think it would make sense to add minimal documentation about running tests in a native image. I guess that would go in the "Running Tests" section, probably under build tools.