Fixed initial setup

...ce/api/src/main/java/at/tuwien/api/error/ApiErrorDto.java

...e/src/main/java/at/tuwien/endpoints/DatabaseEndpoint.java

...rvice/src/main/java/at/tuwien/endpoints/UserEndpoint.java

...c/test/java/at/tuwien/endpoints/UserEndpointUnitTest.java

...st/java/at/tuwien/service/UserServiceIntegrationTest.java

.../src/test/java/at/tuwien/service/UserServiceUnitTest.java

...ices/src/main/java/at/tuwien/gateway/KeycloakGateway.java

...main/java/at/tuwien/gateway/impl/KeycloakGatewayImpl.java

...services/src/main/java/at/tuwien/service/UserService.java

...src/main/java/at/tuwien/service/impl/UserServiceImpl.java

dbrepo-ui/pages/signup.vue

docker-compose.yml