[5.x] Fix taxonomy routes on multi-site

[aerni]

This PR fixes an issue with taxonomy routes on multi-sites. Previously, the taxonomy was accessible on all sites, even on sites that haven't been configured on the taxonomy.

Consider these configs.

resources/sites.yaml

english:
  name: English
  url: /
  locale: en_US
german:
  name: German
  url: /de
  locale: de_DE
french:
  name: French
  url: /fr
  locale: fr_FR

content/taxonomies/tags.yaml

title: Tags
sites:
  - english
  - german

If you've created the necessary views to get the taxonomy routes working, the taxonomy would be accessible on:

• /tags
• /de/tags
• /fr/tags

But the taxonomy was only configured for the english and german sites. This PR fixes this issue. So now the taxonomy is only accessible on:

• /tags
• /de/tags

This fix also applies to collection taxonomy routes. Here, however, the collection's sites will also be considered. In this case, both the taxonomy and the collection need to be configured for the english and german sites.

• /pages/tags
• /de/pages/tags

[aerni]

Hmm, thinking about this a little more, the collection taxonomy routes should probably only be accessible on sites that have been configured on both the collection and the taxonomy. As it stands with this PR, they are accessible for all sites that are configured on the taxonomy. But let's say you have this route /de/pages/tags, you likely want it to throw a 404 if the pages collection or the tags taxonomy isn't configured for the german site.

[jasonvarga]

Yes that sounds right. 👍

[jasonvarga]

I think I meant "Set all the slugs to match the taxonomy collection"