feat: add custom entrypoint script for additional Ruby gems (#63)

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.

Reviewed-on: #63

apps/base/puppet/kustomization.yaml

@@ -54,3 +54,8 @@ configMapGenerator:
       - resources/cobbler-enc
     options:
       disableNameSuffixHash: true
+  - name: additional-ruby-gems
+    files:
+      - resources/additional-ruby-gems.sh
+    options:
+      disableNameSuffixHash: true