Merge did:health driver into universal resolver

[did-health]

merge main

[did-health]

This is the universal driver for did:health. This is part of the DIF Identity Hackathon submission.

[peacekeeper]

Hello, I just tried this and get an HTTP 200 response, but the DID document seems to be empty:

{
  "@context": "https://w3id.org/did-resolution/v1",
  "didDocument": {},
  "didResolutionMetadata": {
    "pattern": "^(did:health:.+)$",
    "driverUrl": "http://driver-did-health:8080/1.0/identifiers/",
    "duration": 25,
    "did": {
      "didString": "did:health:000005saasas1234",
      "methodSpecificId": "000005saasas1234",
      "method": "health"
    },
    "contentType": "application/did+ld+json"
  },
  "didDocumentMetadata": {}
}

Is this expected? Do you have a test identifier that returns an actual DID document when resolved?