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
issue