Add an example of a list of custom roles when using Keycloak DevServices

[danielpetisme]

Description

Keycloak DevServices permit to define a custom role map.
1- Map properties are not obvious for new users
2- There are no details on how to create a list of roles for a given user. A naive guess is to use the comma as a role separator but an explicit mention would help.

https://quarkus.io/guides/security-openid-connect#quarkus-oidc_quarkus.keycloak.devservices.roles-roles

The documentation should either provide an example like:

%dev.quarkus.keycloak.devservices.users.duke=dukePassword
%dev.quarkus.keycloak.devservices.roles.duke=reader
%dev.quarkus.keycloak.devservices.users.quarkus=quarkusPassword
%dev.quarkus.keycloak.devservices.roles.quarkus=reader,writer

or explicit these elements in the property's doc.

Implementation ideas

No response

[quarkus-bot]

/cc @pedroigor, @sberyozkin, @stuartwdouglas