[FEAT] Add integration tests to detect breaking changes with new keycloak versions

**Is your feature request related to a problem? Please describe.**
We don't check if the plugin is compatible with new keycloak versions

**Describe the solution you'd like**
- Add some integration tests (plugin is deployed, FC theme works, plugin configuration is ok, ...) using Keycloak TestContainers dependency (it starts a Keycloak container only for testing)

- Retrieve Keycloak existing versions (using Docker Hub Api: https://hub.docker.com/v2/repositories/jboss/keycloak/tags/?page_size=100)

- Execute tests foreach Keycloak Docker Image (from 9.0.2 to latest)

- Trigger Github actions workflow every week