Add customizable user roles (#18641)

* Add customizable user roles

* Various fixes and improvements

* Add migration for old settings and fix tootctl role management

app/policies/user_role_policy.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+class UserRolePolicy < ApplicationPolicy
+  def index?
+    role.can?(:manage_roles)
+  end
+
+  def create?
+    role.can?(:manage_roles)
+  end
+
+  def update?
+    role.can?(:manage_roles) && role.overrides?(record)
+  end
+
+  def destroy?
+    !record.everyone? && role.can?(:manage_roles) && role.overrides?(record) && role.id != record.id
+  end
+end