UI VSA delete value stream

What does this MR do?

This MR requires the API endpoint added in !41057 (merged)

Adds the relevant UI changes for deleting a value stream

• Allows deletion of any custom value stream
• Updated specs for the value_stream_select component

Screenshots

Default value stream selected	Custom value stream	Delete confirmation	Deleted	With an error

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 Click Create new value stream button from the dropdown next to the title to create a value stream
4. Refresh the page and select your new value stream
5. Open the dropdown and scroll to the bottom to see a button to delete the currently selected value stream (except for default)
6. Click the delete button and confirm

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 #221205 (closed)