VSA settings: [FE] Migrate add / edit value streams to settings page

Proposal

We're moving the VSA value stream configuration / settings from the modal to a standalone settings page.

• This issue is targeted at moving the existing functionality i.e. screenshots below minus the projects / timespan and labels sections.

Vision

New	Edit

Implementation guide

• Move create value stream functionality to a new page /groups/gitlab-org/-/analytics/value_stream_analytics/value_streams/new
• Move edit value stream functionality to a new page /groups/gitlab-org/-/analytics/value_stream_analytics/value_streams/<value-stream-id>/edit
• Clean up old VSA vuex store + update feature tests and jest tests
• Move action buttons to a sticky footer

Additional Notes

• We should be able to re-use the same form for creating and editing
• Create value stream: should redirect to the new value stream on success (/groups/gitlab-org/-/analytics/value_stream_analytics/value_streams/<new-value-stream-id>
• Edit value stream: should stay on the edit page on success
• The action buttons should be added to a sticky footer (see images)
• Ignore selected projects, time period and filters fields for now