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

app/policies/report_policy.rb

@@ -4,4 +4,4 @@ class ReportPolicy < ApplicationPolicy
   end
 end
 
-ReportPolicy.prepend_mod_with('Enterprise::ReportPolicy')
+ReportPolicy.prepend_mod_with('ReportPolicy')