[FE] Create new value stream

What does this MR do?

Required BE changes: !36658 (merged)

• Adds API request to persist new value streams
• Adds vuex action to submit value stream
• Update specs

No changelog added since this is behind a feature flag

Testing

1. Enable value_stream_analytics_create_multiple_value_streams
2. Browse to group VSA, for example /groups/gitlab-org/-/analytics/value_stream_analytics
3. The Create new value stream button should appear next to the title
4. Clicking Create new value stream will display a modal
5. Submitting the modal will display a successful toast message

Note: selecting a value stream will be handled in a separate issue

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #221202 (closed)