fix: canonical URLs in the Partner app

[iskounen]

This PR updates the PartnerMeta component to use the router's current URL to set the canonical URL for each of the sub-pages in the Partner app:

1. /partner/:partnerId/shows
2. /partner/:partnerId/viewing-rooms
3. /partner/:partnerId/works
4. /partner/:partnerId/artists
5. /partner/:partnerId/articles
6. /partner/:partnerId/contact

Each of these is currently referencing /partner/:partnerId as its canonical URL, and after this PR they will each be self-referencing instead. For those pages with pagination, the page=N query param will be included in the URL for pages > 1.

---

This PR also sneaks in a refactor. I noticed that there is some logic to set the canonical URL to an artist's page when an artistId is present in the URL. However, the route that anticipates an artistid is redirecting to the /partner/:partnerId/artist#:artistId route without rendering, so this is dead code:

{
  path: "artists/:artistId",
  render: ({ match }) => {
    // Legacy path: redirect to hash-based anchor
    throw new RedirectException(
      `/partner/${match.params.partnerId}/artists#${match.params.artistId}`,
      301,
    )
  },
},

cc: @artsy/diamond-devs

[iskounen]

This is the scenario that I am refactoring out. I don't believe that this code is reachable now that /partner/:partnerId/artists/:artistId is (301) redirecting to /partner/:partnerId/artists#artistId.

[anandaroop]

Works for me.