Change value stream dashboards URL

What does this MR do and why?

• Rename route for value stream dashboards from /analytics/dashboards to
  /analytics/dashboards/value_streams_dashboard.

related to #390384 (closed)

How to set up and validate locally

1. Make sure you have an ultimate license
2. Enable group_analytics_dashboards_page feature flag
3. Visit http://127.0.0.1:3000/groups/GROUP_PATH/-/analytics/dashboards/value_streams_dashboard

VSD should render.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.