Update selected value stream after deletion or creation

What does this MR do?

This MR Addresses #263392 (closed) and #267008 (closed)

• Ensure we clear the selected value stream after deletion
• Ensure we set the newly created value stream after creation

Testing

1. Enable the value_stream_analytics_create_multiple_value_streams feature flag
2. Navigate to group VSA http://localhost:3001/groups/gitlab-org/-/analytics/value_stream_analytics
3. Create a custom value stream
4. Your new stream should be selected
5. From the value stream dropdown, delete a value stream
6. A new value stream will be selected (or the default) if you only have 1 left

Screenshots (strongly suggested)

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 #263392 (closed)