Create basic Spring Boot Application

[RunCor399]

Description

Create a basic Spring Boot Application that has a few test endpoints and uses Spring Security to interact with a Keycloak instance.

Definition of Done

• The app allows to register and authenticate users against Keycloak
• The app has an endpoint that takes care of generating CoTurn credentials based on the shared secret set up on CoTurn (can be initially mocked until this secret will be effectively shared by CoTurn and Spring)