[FIX] Prevent users to edit an existing role when adding a new one with the same name used before.

[dougfabris]

Proposed changes (including videos or screenshots)

before

after

Issue(s)

Steps to test or reproduce

• Go to admin and permissions
• Try to create a role with the same name as another one already created
• You're going to see the error toast message

Notes for QA

We replaced all of the methods to manipulate the roles. Would be nice to include some tests like:

• Create a new role
• Update a role
• Delete a role
• Check if it's possible to check the users in the role

Further comments

[pierre-lehnen-rc]

The tests are going to pass once #22799 is merged;