Docs: Feedback for Using Variables

Hi, I have some feedback about [this page](https://github.com/hazelcast/imdg-docs/blob/v4.2/docs/modules/configuration/pages/using-variables.adoc)

The pages says `// fill the properties, e.g., from database/LDAP, etc.`

This isn't possible when using Spring. It generates a cyclical dependency since Hibernate forces JPA to load second. People have written issues about this cyclical dependency, and it's not fair to document that a person can load properties from the database. I really wish I could, and I had to refactor to make my settings static :(