OZG-3961 optimize code

.../ozgcloud/operator/keycloak/user/KeycloakUserService.java

...de/ozgcloud/operator/keycloak/user/UserNameConverter.java

...de/ozgcloud/operator/keycloak/user/UserSecretBuilder.java

...de/ozgcloud/operator/keycloak/user/UserSecretService.java

...cloud/operator/keycloak/user/KeycloakUserServiceTest.java

...zgcloud/operator/keycloak/user/UserNameConverterTest.java

...zgcloud/operator/keycloak/user/UserSecretBuilderTest.java

...zgcloud/operator/keycloak/user/UserSecretServiceTest.java