Store public item/record data

[gdethier]

• Story https://github.com/logion-network/logion-internal/issues/948 requires that all public data related to items and records are submitted to the backend, otherwise hashing them on-chain would lead to a data loss
• Public data are submitted to backend before extrinsic submission in order to prevent concurrent updates (sync and client) and the potential data loss this represents (sync does not have the public data anymore, while client does).
• If extrinsic submission fails, submitted public data must be discarded.
• As a result, file upload is simplified: the collection items and tokens records always exist in the DB on upload (but have no CID as long as the file has not been uploaded).
• The mechanism has been implemented for collection items and tokens records.

logion-network/logion-internal#952

[benoitdevos]

Good job !