Tasks:

• add a new collaborator to a map
• remove collaborators from a map
• get all collaborators for a map
• search for users by username

Notes:
All those endpoints need to communicate with Keycloak, because they need data that is stored there (username).
For this we will use the Keycloak Admin REST API.
https://www.keycloak.org/docs-api/21.1.1/rest-api/