Create / Edit value stream bugs

Summary

Documenting some potential backend issues encountered with the edit value stream form

• Adding a new stage when editing an existing value stream fails
• Changing the name of default stages - disabled for now
  • Default value stream with edited stage names - see #329282 (closed)
  • Stage name has already been taken error - see #329283 (closed)
• Editing the order of stages is not reflected - see #321751 (comment 562126117)

* [ ] Hidden default stages cannot be restored when editing - moved this to #325990 (closed)

Steps to reproduce

1. Enable the value_stream_analytics_extended_form feature flag
2. Steps are documented on the relevant threads below

What is the current bug behavior?

These are bugs that have been observed locally, it would be good to validate they are occurring for others and also on staging. Note the form is currently behind the :value_stream_analytics_extended_form feature flag which is only enabled on staging.

Possible fixes