BACKEND: todo's that didn't make it into the final release

[DanielHabenicht]

• [x] Health Endpoint (/health - return 200) @paule96
• [x] Add health endpoint to helm chart
• [ ] Caching Header (client-side) @paule96
• [ ] Remove Messenger @DanielHabenicht
• [x] Create new docker image tsystemsmms/phonebook-source-peoplesoft in dockerhub @jandd
• [x] Publish new image to tsystemsmms/phonebook-source-peoplesoft
• [ ] Set up versioning
• [ ] ~~Add preview to environment (maybe same as development)~~
• [x] decrease Developlment mock data to 1500
• [x] use seed for mock data, so that ids stay the same

Optional (maybe refactor into another issue, to close this one:

• Caching (locally, inside the server)
• New Version of the Endpoint for better data sources)

[jandd]

created https://hub.docker.com/r/tsystemsmms/phonebook-source-peoplesoft

[paule96]

The work for the health check is done. Please review it here: #601