In the current implementation, the AssetProvider defines the supported metadata (AssetProvider#supports(Class<? extends AssetMetadata> metaData))

We should also have a way to retrieve the list of supported metadatas.

In addition, we should also have this on Asset. An AssetProvider may support 2 or 3 metadata Type, but a given Asset may only support one Type (a document and video Asset may not support the same metadata Type).