Repair broken Collection URL and add to tests

[anjackson]

The ukwa/ukwa-ui:v1.4.0 release has broken this link https://dev.webarchive.org.uk/en/ukwa/collection and replacing it with https://dev.webarchive.org.uk/en/ukwa/category

1. This should have been caught by the tests, so add it there.
2. The website NGINX configuration should be updated to redirect .../collection to .../category.

[anjackson]

Hmm, this is returning a 500 rather than a 404 so moving here to clarify whether it should be working.