Bug: Unable to add roles to users

[wz2k]

Steps to reproduce

1. As an administrator navigate to the manage users page
2. For any user in the table, click on the plus icon to under roles
   
3. Fill in role information and attempt to add the role

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Error description

The following notification will be shown when attempting to add a role:

The cause of this is a 404 not found error for the endpoint.

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Possible fix

There is a /api/users/:variable endpoint for adding multiple roles when variable = one of the role names. The endpoint also adds a role to a single user if variable is a user ID. Currently, the frontend for adding roles tries to send data to the /api/users/:userId/:role endpoint, which does not match. Removing /:role would match the endpoint, but changes need to be made to the request body being sent for it to work.