chore: Clean up report & knowledge base policies (#11234)

- Removes the portal_members table and all associated records
- Updates policies to use custom roles with knowledge_base_manage
permission
- Updates controllers, models, and views to work without portal
membership
- Adds tests for the new permission model

config/routes.rb

@@ -264,7 +264,6 @@ Rails.application.routes.draw do
           resources :portals do
             member do
               patch :archive
-              put :add_members
               delete :logo
             end
             resources :categories