Fix a document 404ing with a redirect
user
```ruby
require 'gds_api/router'

router = GdsApi::Router.new(Plek.current.find('router-api'))

not_found_slug = "/government/publications/vat-notice-7002-group-and-divisional-registration/vat-notice-7002-group-and-divisional-registration"
content_at_slug = "/government/publications/vat-notice-7002-group-and-divisional-registration/vat-notice-7002-group-and-divisional-registration--2"

puts "registering redirect #{not_found_slug} -> #{content_at_slug}"
router.add_redirect_route(not_found_slug, 'exact', content_at_slug)
puts "done registering redirect"
```
assistant