feat: add from record method to cred preview

[TimoGlastra]

Two api improvements

1. register credential definition doesn't require signatureType parameter anymore (just add bloat to the API)
2. add fromRecord method to credential preview to be able to create a preview from json object. this makes it a lot simpler:

Before

const credentialPreview = new CredentialPreview({
  attributes: [
    new CredentialPreviewAttribute({
      name: 'name',
      mimeType: 'text/plain',
      value: 'John',
    }),
    new CredentialPreviewAttribute({
      name: 'age',
      mimeType: 'text/plain',
      value: '99',
    }),
  ],
})

After

const credentialPreview = CredentialPreview.fromRecord({
  name: 'John',
  age: '99',
})

[codecov-commenter]

Codecov Report

Merging #428 (9d9cf84) into main (0e2338f) will decrease coverage by 0.63%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #428      +/-   ##
==========================================
- Coverage   86.24%   85.61%   -0.64%     
==========================================
  Files         249      249              
  Lines        5264     5346      +82     
  Branches      784      798      +14     
==========================================
+ Hits         4540     4577      +37     
- Misses        724      769      +45     

Impacted Files	Coverage Δ
.../modules/credentials/messages/CredentialPreview.ts	84.61% <100.00%> (+2.79%)	⬆️
packages/core/src/modules/ledger/LedgerModule.ts	90.00% <100.00%> (ø)
packages/core/src/agent/MessageSender.ts	71.92% <0.00%> (-2.30%)	⬇️
packages/core/src/agent/Agent.ts	94.68% <0.00%> (-2.20%)	⬇️
.../core/src/modules/connections/ConnectionsModule.ts	72.15% <0.00%> (-1.88%)	⬇️
...ckages/core/src/transport/WsOutboundTransporter.ts	3.94% <0.00%> (-1.32%)	⬇️
...ckages/core/src/modules/routing/RecipientModule.ts	63.04% <0.00%> (-0.96%)	⬇️
.../modules/connections/models/did/service/Service.ts	100.00% <0.00%> (ø)
.../modules/connections/services/ConnectionService.ts	98.83% <0.00%> (+0.01%)	⬆️

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[berendsliedrecht]

Once test passes, I will merge.

[jakubkoci]

I like this improvement. I would consider calling it fromJSON to prevent confusion with other framework's records, that's what I would expect as a consumer at least.

To me, the best API would be just passing JSON objects, but this is definitely step forward 👍

[TimoGlastra]

The problem with fromJSON is that it clashes with toJSON.

Currently, toJSON transforms the class instance to the JSON representation. If we have a fromJSON method, I'd expect it to be the exact opposite of toJSON. Which it is not.

The reason I didn't change the constructor is because the fromRecord method removes the option to set a mime-type. Most time we just use text/plain, but it should be possible to set it

[TimoGlastra]

I'm not set on fromRecord, so if you have suggestions I'm happy to create a new PR