Refactor Admin listRoles function to remove tenant related information

[mikelax]

Feature Overview

Is your feature request related to a problem? Please describe.

Currently, in the database listRoles function there is a case where the same role can be returned multiple times in the response. This can happen if the role belongs to a client, and this client is associated with multiple tenants.

Describe the solution you'd like

Refactor the function to remove the join condition to the tenants table and remove the tenant attributes from the response. In the scope of a Role object, the concept of tenant attributes doesn't actually make sense to include and confuses the function response.

Additional context

See this conversation in #126 for additional information and discussion.