Expose metadata as part of the state

[dr-orlovsky]

Currently, RGB Node nodes not provide an API to access metadata of the contract nodes. The rationale was that it is impossible to detect whether metadata in a node are invalid/replaced with a new metadata of a node descendant: each node may have zero to many descendants and it is impossible to define a rules for state invalidation without the use of single-use-seals (which are not used for the metadata).

It was intended that all state should be defined with single-use-seal-based owned state mechanism. However, certain scenarios make this definition impossible: for instance, when the state is updated by the state transition which does not allow further state modification and, thus, does not defines new single-use-seals.

To cover such cases (which include a case of asset naming and renomination for RGB20 and RGB21 schemata) it is advised to expose an API which will return a metadata for a given contract node ID. This will allow client libraries to do a custom state conflict resolution and apply schema-specific logic to access particular metadata (such as asset name).

[dr-orlovsky]

A way towards the solution: RGB-WG/rgb-core#117