chore: add medium/genre to metadata

[nickadamson]

Describe the solution you'd like
Whether by genre, medium, or even hashtags - there needs to be a way for creators to categorize their mints.

Describe alternatives you've considered
Either emitted during transaction for logging by subgraph, or directly in metadata before uploading to IPFS.

Additional context
Will be used in front end for sorting by chosen breakdown. Would like to have a dialogue about it.

[nickadamson]

https://github.com/nickadamson/media-metadata-schemas/tree/master/schemas

[nickadamson]

schema is here: https://github.com/nickadamson/media-metadata-schemas/blob/master/schemas/ourz/20210928.json

just about finalized