Use strings as properties key in kubernetes service spec.

What does this MR do?

The specs for rails 4 already worked with wrong properties value e.g. from line 108:

kubernetes_service.properties => {"api_url"=>"https://kubernetes.example.com", "token"=>"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "namespace"=>nil, :namespace=>"foo"}

A save does not deletes the keys from the object in Rails 4(both "namespace" and :namespace are in the properties hash). Rails 5 deletes the properties that it can't save, so the spec fails(only "namespace" is kept). I changed the spec to using a string instead of a symbol, just like it is everywhere that a service properties hash is used.

Are there points in the code the reviewer needs to double check?

I changed all wrong usages of properties with a symbol, not only the ones that fail in the Rails5 specs.

Why was this MR needed?

rails5 upgrade

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Fix for #46230 (closed).