Web dids

[IanCal]

Adds basic support for resolving web dids. Tests should mock out the remote request but don't currently.

Web dids have a structure of:

did:web:domain

which will try and find a document at https://domain/.well-known/did.json

Or

did:web:domain:subfolder:subfolder2

which will try and find one at https://domain/subfolder/subfolder2/did.json

It's a bit inconsistent but that's how it goes.

I've put sample ones at

https://superb-conkies-141fd5.netlify.app/.well-known/did.json

and

https://superb-conkies-141fd5.netlify.app/subfolder/did.json

Which also show the two ways that should now be supported for pointing at resources - one uses alsoKnownAs and the other a service endpoint:

  "service": [
    {
      "id": "did:web:example.com#resource1",
      "type": "ResourceService",
      "serviceEndpoint": "https://superb-conkies-141fd5.netlify.app/testme"
    }
  ]```

[github-actions]

ssr-web test results

180 tests  ±0   180 ✔️ ±0   11s ⏱️ -1s
    1 suites ±0       0 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 4591821. ± Comparison against base commit 7138a1b.

♻️ This comment has been updated with latest results.

[github-actions]

web-client test results

528 tests  ±0   528 ✔️ ±0   1m 16s ⏱️ +9s
    1 suites ±0       0 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 4591821. ± Comparison against base commit 7138a1b.

♻️ This comment has been updated with latest results.

[tintinthong]

lgtm. Will add stuff as part of my testing and explanation in separate prs.