Since the role creation flow will involve more than one screen, I believe it is necessary (or good to have since it's extendable) to have a `role-navigator` that will handle its related routes. This
diff creates the navigator, and the next few diffs in the stack will use this for navigation. I mainly used the invite links navigator & the community creation navigator as inspiration here.
Depends on D8333
[[ https://linear.app/comm/issue/ENG-4167/create-a-roles-navigator-to-handle-the-role-creation-flow | ENG-4167 ]]