[BE] Multiple value streams: Create new value stream MVC

Explanation

This is the backend implementation issue for creating a new value stream. frontend work is being tracked in #221202 (closed)

Problem to Solve

This issue focuses on allowing users to create new value streams:

• Broken down from: #219106 (closed)
• Job-to-be-done: Create a saved view. When managing multiple value streams within a mono-repo, I would like to create and save a view of my value stream, so that I can come back to it regularly.

Proposal

• When a user clicks to create a new Value Stream, the default template should be duplicated, then the user can customize it.
• User flow see Figma prototype:
  1. "Create new value stream"
     • If there aren't multiple value streams, display Create new value stream button
     • If there multiple value streams, display Create new value stream as an option in the dropdown section
  2. Pop up a modal to confirm and capture name
  3. Display new value stream with toast message (3000ms) to confirm creation

Button	Modal	Toast

See Figma file

Out of scope

Switching between multiple value streams is handled in: #221204 (closed)

Permissions and Security

• Permissions for creating new Value Streams is the same as those for configuring them generally.

Feature Flag

• Initially, make available to gitlab-org group on gitlab.com
• After PM request, make more broadly available from internal users and addressing any concerns about scaling.

What is the type of buyer?

• This feature will be made available in GitLab Ultimate