Add did:unitrust method

[zengmenglu]

DID Method Registration

As a DID method registrant, I have ensured that my DID method registration complies with the following statements:

• The DID Method specification defines the DID Method Syntax.
• The DID Method specification defines the Create, Read, Update, and Deactivate DID Method Operations.
• The DID Method specification contains a Security Considerations section.
• The DID Method specification contains a Privacy Considerations section.
• The JSON file I am submitting has passed all automated validation tests below.
• The JSON file contains a contactEmail address [OPTIONAL].
• The JSON file contains a verifiableDataRegistry entry [OPTIONAL].

[msporny]

Meets minimum requirements for registration.

[gatemezing]

Meets minimum requirements for registration.

[zengmenglu]

Hello, @msporny @gatemezing , I wanted to check if there are any additional steps we need to take before the PR can be merged. Please let us know if there's anything further required from our side. Thank you!

[genaris]

@msporny now that this PR received 3 approvals are we good to merge, right?

If so, @zengmenglu can you update your branch so it is ready to be merged? Thanks!