Update VerifiableCredentialBuilder

[andresuribe87]

The spec states that id is optional. If present, it must be a URL, which may be dereferenced.

To better support the spec, we should update the sdk such that:

• The default ID is empty (to foster stronger privacy).
• Update the method SetID(), so it does validation that the parameter is a URI (using the url.Parse function).

[decentralgabe]

Example id values include UUIDs (urn:uuid:0c07c1ce-57cb-41af-bef2-1b932b986873), HTTP URLs (https://id.example/things#123), and DIDs (did:example:1234abcd).

since we use UUIDs we'll probably want to update to add the urn:uuid prefix

[m-rit]

@decentralgabe, can I work on a PR to to add this fix if no one is working on it? I've used this repo for a personal projects and I'd like to contribute to the issues.

[decentralgabe]

@m-rit yes definitely

most of the work at TBD has moved to https://github.com/TBD54566975/web5-go, though I still use this SDK sometimes

[m-rit]

I have raised a PR to address the issue, NewVerifiableCredentialBuilder now creates VC with empty ID. Should I add an option argument in the function to aupport VC creation with new uuid (the original behaviour) ?

[decentralgabe]

@m-rit yes!