[Documentation] Add differnt ways of using keycloak security

### Relevant documentation

Other

### Problem description (optional)

The Keycloak and Spring security can be used in different ways, depending on what is needed. We need to document the different ways

### Desired solution

add the following concepts to the documentation for keycloak security:
- roles
- use-case roles
- application roles

### Additional context (optional)

- Internal discussion: https://git.muenchen.de/ccse/Architekt_innenrunde/-/issues/161

### No duplicate

- [x] I confirm that this issue is not a duplicate

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Start by reviewing the existing Keycloak and Spring Security documentation and the linked internal discussion, issue 161. Document the roles, use-case roles, and application roles, clearly explaining the different ways of using Keycloak security; done means all three requested concepts are covered.

Written by the indexing model from the issue text.