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

spec/models/portal_spec.rb

@@ -12,8 +12,6 @@ RSpec.describe Portal do
     it { is_expected.to have_many(:categories) }
     it { is_expected.to have_many(:folders) }
     it { is_expected.to have_many(:articles) }
-    it { is_expected.to have_many(:portal_members) }
-    it { is_expected.to have_many(:members) }
     it { is_expected.to have_many(:inboxes) }
   end