Standardized approach for allowing third party access to media files for ERC721 NFTs

Issue can be used as discussions code review for the suggested standardized approach for allowing third party access to media files for ERC721 NFTs

Main documentation:
https://meebitsdao.github.io/erc721-media-api/
(generated from [OpenAPI contract](https://github.com/MeebitsDAO/erc721-media-api/blob/main/openapi-contract/api-contract.yaml))