Refresh collection metadata

Queue a re-read of the collection's contract-level metadata, such as the name, description and image from contractURI(). Items with missing metadata are refetched too; to refresh one item use POST /api/v2/chain/{chain}/contract/{address}/nfts/{identifier}/refresh. The refresh runs in the background, so GET /api/v2/collections/{slug} shows the result after it finishes. Only the collection owner or an authorized editor can request it.

The contract-level metadata (contractURI() for most EVM contracts) wins for the fields it sets: a name, description, image or banner in it replaces the value saved with PATCH /api/v2/collections/{slug}, while a field it leaves out or blank keeps the saved value. Page content saved with PATCH /api/v2/collections/{slug}/metadata is kept the same way: the overview and about sections are kept, and hero and preview media are kept unless the refresh fetched its own for that slot, which then replaces the saved one.