Add custom roles to Role-based access control extension

[ghost]

Is your feature request related to a problem? Please describe.
Currently, RBAC has only 4 predefined roles that you cannot modify. Being able to create and modify user roles would mean administrators have more fine-grained control over their user's abilities.

Describe the solution you'd like
Within the roles view, add the ability to create and modify roles & their abilities against each resource in Portainer.

[coreydavis-emerson]

i fully support this idea