[ENHANCEMENT] add functionality for custom role bindings for a specific user in 8.8 basic auth

[hamza-m-masood]

Describe the use case:

Currently in 8.8, while using basic auth, all users are assigned the admin role.
It is already possible to assign custom roles to users in the core configmap like so:

camunda:
  security:
    initialization:
        default-roles.connectors.users:
          - "lisa"
        default-roles.rpa.users:
          - "demo"

This functionality is not supported in the values.yaml.
When defining a user, it would be better to also define the custom roles of that user as well.

Describe the enhancement/feature:

The challenge here is to find a good non-breaking syntax that would work in the values.yaml and would then get translated to the core configmap syntax above.

Desired outcome and acceptance tests:

[hamza-m-masood]

@hisImminence will have a meeting with Mattia, about the unified config.