GET /roles

Apart of the V2 API work, we need a GET "roles/" endpoint for listing all system roles (platform +seeded) and custom roles.

Requirements:

• Support fuzzy search by role name
• Support sorting by role name and last modified timestamp

Acceptance Criteria:

• API spec should take implementation into consideration
• API should be consistent with other RBAC V2 APIs
• Shared in the team-mgmt-fabric channel and reviewed by architects and leads
• Have to consider this: https://issues.redhat.com/browse/RHCLOUD-37863