[VSA] - Hidden stages still show in the form

Problem

After a custom value stream has created its own stages and hidden some default stages, there is a bug where the hidden stages are still shown in the edit value stream modal.

This can be reproduced on this page: https://gitlab.com/groups/gitlab-org/-/analytics/value_stream_analytics?created_after=2021-02-24&created_before=2021-03-25&value_stream_id=491

Proposal

Hidden stages should be listed at the bottom of the edit view form...