[Uniques V2] Smart attributes

[jsidorenko]

This PR adds a new feature called Smart Attributes.
The main idea of that feature is to allow an owner of an NFT to allow other entities (e.g. another account, an application, a parachain, a custom origin, etc.) to update certain attributes about the NFT. For example, a member of the Polkadot Technical Fellowship could have a membership badge that evolves over time by giving the Fellowship origin permission to update its attributes (e.g. Rank) on the badge directly.

On a technical level to achieve all that I decided to prefix attributes with the namespace.
Currently, 4 different namespaces were created:

• Pallet(PalletId) - which means the attribute was set and could be changed by the pallet only;
• CollectionOwner - means the attribute can be set and modified by the collection's owner only;
• ItemOwner - a namespace for the NFT owners. This is an ideal place to store some custom values like dapps preferences, dids, NFT's custom title, etc.;
• Account(AccountId) - attributes within that namespace could be modified only if the origin was given permission to do so.

To control whether an external account could modify attributes within its namespace the new methods were added:
approve_item_attributes and cancel_item_attributes_approval. When the permission gets revoked, all the previously set attributes by that account will be removed.

[jsidorenko]

bot merge