Simplify configuring cluster roles for Che users

[tolusha]

Is your task related to a problem? Please describe

The current workflow is complicated and includes che-server component to configure additional roles for a users [1]
It was actual when che-server engine was used instead of devWorkspace one.

[1] https://eclipse.dev/che/docs/stable/administration-guide/configuring-cluster-roles-for-users/

Describe the solution you'd like

• Remove che-server component from equation.
• Use Configuring a user namespace feature [1]
• Update the documentation
• Check if actually Roles exist before delegating

[1] Configuring a user namespace

Describe alternatives you've considered

No response

Additional context

No response