[ENH] - Parse and load keycloak roles into JupyterHub

[aktech]

Feature description

After the issue #2308 is implemented, we will have access to groups and roles from keycloak in JupyterHub. Next we need to parse the role attributes and load them into JupyterHub, so that those permissions scopes are actually in affect in JupyterHub.

For example, consider the following role in Keycloak:

Role: allow-app-sharing-role

The role attributes (in keycloak) for the above mentioned role:

Key	Value
resource	jupyterhub
scopes	shares!user,read:users:name,read:groups:name

The value for scopes defined above is (and must be) a valid syntax for scopes in JupyterHub. When these are applied, the users in that group should have permissions to share an app(or server).

Let's take another simpler example (that can be used as a motivating example for the implementation of this issue):

Role: read-only-user-models

The role attributes (in keycloak) for the above mentioned role:

Key	Value
resource	jupyterhub
scopes	read:users

This role allows users/groups (when attached this role) to read (but not modify) any user’s model. This example is taken from: https://jupyterhub.readthedocs.io/en/latest/rbac/roles.html#defining-roles

This feature is part implementation of RFD: nebari-dev/governance#47

Value and/or benefit

This will allow us to do fine-grained permissions on JupyterHub, which can be controlled from keycloak.

Anything else?

No response

[aktech]

Unblocked now, since #2447 is merged.