User Provided Metadata JSON URI

[kespinola]

Goal

Users can provide the metadata URI to mintToCollection Mutation.

Requirements

• Make MetadataJsonInput optional
• Add optional metadataUri: Uri input option to MintToCollectionInput
• Validate that user provides either metadataJson or metadataUri
• When the user specificies metadataUri fetch the contents of the uri and write metadata json records