feat: add custom entrypoint script for additional Ruby gems

Add support for installing additional Ruby gems via custom entrypoint script.
The script is mounted as a ConfigMap into /container-custom-entrypoint.d/
and will be executed during Puppetserver container startup.

apps/base/puppet/deployment_puppetserver-compiler.yaml

@@ -99,6 +99,9 @@ spec:
         - mountPath: /opt/vault-ca-cert.crt
           name: vault-ca-cert
           subPath: ca.crt
+        - mountPath: /container-custom-entrypoint.d/additional-ruby-gems.sh
+          name: additional-ruby-gems
+          subPath: additional-ruby-gems.sh
       initContainers:
       - name: copy-configmaps
         image: busybox:1.35
@@ -235,5 +238,9 @@ spec:
       - name: vault-ca-cert
         secret:
           secretName: vault-ca-cert
+      - name: additional-ruby-gems
+        configMap:
+          name: additional-ruby-gems
+          defaultMode: 0755
   strategy:
     type: RollingUpdate