The QE review of 3.2.8 product docs highlighted some missing content that would be helpful for folks unfamiliar with enabling Basic authentication in Quarkus.

This PR:

• Enhances the prereq to clarify two extensions that can be used to enable Basic authentication.
• Adds a new step (number 2) for setting the configuration option `(quarkus.security.users.embedded.enabled=true)` , which is needed to enable the security via the embedded realm.

:eyes: @jsmrcka & @sberyozkin (REF QUARKUS-3651)