Establish test runners for serverless logic tooling - vscode extension

Summary
Implement test runner for vscode extension of serverless diagram editor.
There should be a test suite that simulates use cases of our users in VSCode.
Former knowledge from BPMN testing is to be used.

Goals
Implement a test suite in `vscode-extension-serverless-workflow-editor`.
Have the tests controlled by a system property.
Introduce basic example test.

Acceptance criteria
Test suite is merged into the upstream.
Basic example test is present.