Iris: Create and call endpoint to check if Iris is active

[SolizerCodes]

Checklist

General

• This is a small issue that I tested locally and was confirmed by another developer on a test server.
• Language: I followed the guidelines for inclusive, diversity-sensitive, and appreciative language.
• I chose a title conforming to the naming conventions for pull requests.

Server

• Important: I implemented the changes with a very good performance and prevented too many (unnecessary) database calls.
• I followed the coding and design guidelines.
• I added multiple integration tests (Spring) related to the features (with a high test coverage).
• I added pre-authorization annotations according to the guidelines and checked the course groups for all new REST Calls (security).
• I documented the Java code using JavaDoc style.

Motivation and Context

We want an endpoint that initially checks if the specific Iris model is active (might change to a websocket connection in the future).

Description

For now adds an endpoint which returns for a session if the model is available.

Testing

Testing if a model is not available is difficult. Try if Iris still works without problems.