Add profile field limits to instance serializer (#37535)

app/serializers/rest/instance_serializer.rb

@@ -71,6 +71,9 @@ class REST::InstanceSerializer < ActiveModel::Serializer
       accounts: {
         max_featured_tags: FeaturedTag::LIMIT,
         max_pinned_statuses: StatusPinValidator::PIN_LIMIT,
+        max_profile_fields: Account::DEFAULT_FIELDS_SIZE,
+        profile_field_name_limit: Account::Field::MAX_CHARACTERS_LOCAL,
+        profile_field_value_limit: Account::Field::MAX_CHARACTERS_LOCAL,
       },
 
       statuses: {