Bump keycloak-services from 16.1.0 to 18.0.0

Bumps [keycloak-services](https://github.com/keycloak/keycloak) from 16.1.0 to 18.0.0.
- [Release notes](https://github.com/keycloak/keycloak/releases)
- [Commits](keycloak/keycloak@16.1.0...18.0.0)

---
updated-dependencies:
- dependency-name: org.keycloak:keycloak-services
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

pom.xml

@@ -9,7 +9,7 @@
     <java.version>1.8</java.version>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <main.java.package>gr.cti.nts</main.java.package>
-    <keycloak.version>16.1.0</keycloak.version>
+    <keycloak.version>18.0.0</keycloak.version>
     <junit.version>4.8.1</junit.version>
     <lombok.version>1.18.12</lombok.version>
     <auto-service.version>1.0-rc7</auto-service.version>