Establish test runners for serverless logic tooling - marshallers roundtrip

Summary
Implement test runners for serverless logic tooling according to test approach discussed on our meetings.
Verify the marshaller roundtrip - Load(setContent()) -> View -> Download(getContent()).

Goals
Implement a test suite in java using selenium.
Put the test suite into serverless-workflow-diagram-editor.
Introduce a JSON validator to check files are not broken after roundtrip.
Create a test-environment using quakus kogito-serverless-workflow mvn archtype.

Acceptance criteria
Test suite is merged into upstream.
There is a sample test for new file & basic example file.