Rename a glossary. The slug and the source language never change, so
stored glossary and term IDs keep working.

Only organization administrators can rename glossaries, and only on a plan
that supports glossary upload.

A 409 means the glossary's stored state refuses the rename: it is
archived or it has no resource. A body whose id names another glossary
than the path gets a 409 too, as JSON:API requires.