Update DID resolver contentMetadata to return {}

[kirahsapong]

From @AlexHsieh in this comment:

Also at reading web5-js, found out that this line

contentMetadata : didResolutionMetadata

should be

contentMetadata : didDocumentMetadata

Someone might help check ? thanks

[kirahsapong]

Update on the above: contentMetadata should be an empty metadata structure {} per the spec:

contentMetadata
If the dereferencing is successful, this MUST be a metadata structure, but the structure MAY be empty.
This structure contains metadata about the contentStream. If the contentStream is a DID document, this MUST be a didDocumentMetadata structure as described in DID Resolution.
If the dereferencing is unsuccessful, this output MUST be an empty metadata structure.

Good catch @frankhinek and @AlexHsieh!