Display the Java classes of an agent to be instrumented

[tingrida]

As a user, I would like to see a list of instrumented Java classes on the detail page of an agent (should state) to get an overview of my current instrumentation area.

Only classes to be instrumented by the Gepard extension are considered here.

After restarting the application, our instrumentation in the agent can be “empty” again.
After leaving the page, the list in the UI may be “empty”.
Both of these steps should be carried out together to ensure consistency (currently).