Add settings endpoints

[Jannik Emmerich]

Is your feature request related to a problem? Please describe.
The frontend has to store some individual user settings in the backend.

Describe the solution you'd like
Add settings endpoints like in the old backend.
Create a Setting data class and a settings endpoint collection inside the daemon with the following endpoints:

• settings/save
• settings/get
• settings/delete

Additional context
The old implementation can be found here:

• Setting.java
• WebSocketHandler.java:103-151