MBS-7493: use rel=canonical to canonicalize our pages

Like it says. Uses 'https://musicbrainz.org' as the canonical server (for beta, slaves, and plain-http MB), and for entities with MBIDs, change to the MBID from the actual table row, on quasi-redirected pages (could do an HTTP redirect instead, but this is much easier).

UPDATE: add instruments, merge in schema branch

UPDATE 2: properly canonicalize multi-argument endpoints. Cue slight annoyance at TT, which doesn't know the difference between an array and an arrayref.