Boilerplate - Create new value stream MVC

What does this MR do?

• Adds the value_stream_analytics_create_multiple_value_streams
• Adds a stub button to create a new value stream (currently does nothing)
• Updated specs

NOTE:

• Displaying the form when clicking the button will be handled in a follow-up MR

Feature flag

Requires the value_stream_analytics_create_multiple_value_streams feature flag

Screenshots

Before	After - xs size	After - other sizes

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

Does this MR meet the acceptance criteria?

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

Related to #221202 (closed)