feat: new component for data models - DIDs, signatures, JSON-LD

[Moopli]

component/models/:

• did: afgo's DID and DID Doc models.
• ld: JSON-LD support - data models, context stores, LD-Proofs, canonicalization, etc.
• signature: signing APIs used in DID Docs etc.
• util: utility data models needed for other model implementations, but not specific to a given model.

[codecov[bot]]

Codecov Report

Merging #3565 (3d0f089) into main (a8b546e) will decrease coverage by 0.53%. The diff coverage is 54.03%.

@@            Coverage Diff             @@
##             main    #3565      +/-   ##
==========================================
- Coverage   87.76%   87.24%   -0.53%     
==========================================
  Files         351      353       +2     
  Lines       48627    48671      +44     
==========================================
- Hits        42677    42461     -216     
- Misses       4402     4673     +271     
+ Partials     1548     1537      -11     

Impacted Files	Coverage Δ
component/models/did/endpoint/endpoint.go	91.50% <ø> (ø)
component/models/did/helpers.go	54.47% <ø> (ø)
component/models/did/legacy.go	92.94% <ø> (ø)
component/models/did/serialize_default.go	100.00% <ø> (ø)
...ponent/models/ld/context/remote/remote_provider.go	79.48% <ø> (ø)
component/models/ld/proof/utils.go	78.84% <ø> (ø)
component/models/ld/store/context_store.go	87.50% <ø> (ø)
component/models/ld/store/remote_provider_store.go	93.87% <ø> (ø)
...e/suite/bbsblssignature2020/public_key_verifier.go	100.00% <ø> (ø)
...te/bbsblssignatureproof2020/public_key_verifier.go	100.00% <ø> (ø)
... and 39 more

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[Moopli]

Note: Since this PR introduces a new component that afgo depends on, it needs a followup that removes the go.mod replace directives (replace github.com/hyperledger/aries-framework-go/component/models => ./component/, etc) and updates imports of component/models to use this PR commit.

[DRK3]

Something else I'm wondering: do we really need individual packages for all the various pieces under component/models/ld? If they're all related, is there a reason to require a caller to import multiple packages? Will anyone need to import one of them but not the other? etc

[Moopli]

If they're all related, is there a reason to require a caller to import multiple packages? Will anyone need to import one of them but not the other?

Hmm so, testutil definitely needs to be separate, and usually only context is imported together with other ld/ packages, so I'm not sure what it gains, while at least right now there's a clear separation of functionality.