Add customizable user roles (#18641)

* Add customizable user roles

* Various fixes and improvements

* Add migration for old settings and fix tootctl role management

app/serializers/rest/role_serializer.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+class REST::RoleSerializer < ActiveModel::Serializer
+  attributes :id, :name, :permissions, :color, :highlighted
+
+  def id
+    object.id.to_s
+  end
+
+  def permissions
+    object.computed_permissions.to_s
+  end
+end