fix: Invalid VC for JWS signature

[bstasyszyn]

The proof for VC now uses the jws field for VCs signed with JsonWebSignature2020. Strict validation was enabled for VC verification.

Also, updated the JSON-LD context for AnchorCredential.

closes #1435

Signed-off-by: Bob Stasyszyn Bob.Stasyszyn@securekey.com

[codecov]

Codecov Report

Merging #1436 (f5c0fe9) into main (c03aff7) will decrease coverage by 0.07%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##             main    #1436      +/-   ##
==========================================
- Coverage   87.93%   87.86%   -0.08%     
==========================================
  Files         208      208              
  Lines       19559    19567       +8     
==========================================
- Hits        17200    17193       -7     
- Misses       1503     1516      +13     
- Partials      856      858       +2     

Impacted Files	Coverage Δ
pkg/activitypub/vocab/vocab.go	100.00% <ø> (ø)
pkg/vcsigner/signer.go	89.10% <80.00%> (+1.48%)	⬆️
pkg/activitypub/vocab/contextproperty.go	95.91% <100.00%> (ø)
pkg/anchor/builder/builder.go	100.00% <100.00%> (ø)
pkg/anchor/handler/credential/handler.go	78.18% <100.00%> (+0.13%)	⬆️
pkg/anchor/handler/proof/handler.go	77.77% <100.00%> (+0.19%)	⬆️
pkg/anchor/writer/writer.go	87.92% <100.00%> (+0.02%)	⬆️
pkg/observer/observer.go	83.62% <100.00%> (+0.05%)	⬆️
pkg/vct/vct.go	86.46% <100.00%> (ø)
...pub/service/inbox/httpsubscriber/httpsubscriber.go	88.88% <0.00%> (-8.89%)	⬇️
... and 4 more

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