Integrate credo for credential operations

[jrhender]

Proposal

Integrate Credo for credential operations.
Link to repository: https://github.com/openwallet-foundation/agent-framework-javascript
Link to docs: https://credo.js.org/

Research

Support for data integrity signature

Credo supports data integrity signatures.
In particular, Ed25519Signature2018 signatures seem to be supported out-of-the-box, which is the main signature type used thus far within the VC API implementation.

Support for JSON-LD VCs

The seems to be support for a document loader which could be used for adding contexts. https://github.com/openwallet-foundation/credo-ts/blob/main/packages/core/src/modules/vc/data-integrity/W3cJsonLdCredentialService.ts#L111

Pros

• Using a project from within the Open Wallet Foundation would allow better synergy
• Would have a clearer path to supporting further VC technology such as SD-JWT and BBS signatures
• Ability to use custom JSON LD Contexts

Cons

• If removing didKit, it could be a breaking change due to differing implementation details in proof issuance and/or verification

TODO

Pre-implementation Research

• decide if we should replace the existing credential operations library (didKit) or try to add Credo alongside
• confirm whether or not additional LD contexts are supported by Credo (seems promising with document loader available)
• check if/how Credo supports key creation/utilization at runtime
• consider if it makes more sense to try to get VC API directly into Credo

Implementation Steps

• replace didKit with credo. The credential.service is where didKit is currently integrated. I believe this is the core file that would need to be changed
• adjust documentation to explain why credo is now being used -> This should include the additional of an ADR
• adjust documentation to use context file links

[jrhender]

Completed by #38 . #39 opened to complete outstanding documentation fix.