This change adds configurable settings to the `CustomRealm` in the QA
project as the correct declaration and use of settings can be a source
of confusion in custom realms.
The "username" "password" and "roles" are now all configurable, which
demonstrates the use of a simple string setting ("username") a secure
setting ("password") and a more complex list setting ("roles").
Backport of: #62287
eeb45b4a74