Use keyRef if supplied to pick signing key in `createVerifiablePres…

[jasny]

What issue is this PR fixing

https://github.com/uport-project/veramo/blob/6981e6845d6f90d7b0c8dd6e0117b73dfd8edfb9/packages/credential-w3c/src/action-handler.ts#L240-L242

keyRef is an arg property for createVerifiablePresentation and createVerifiableCredential. It should be used to pick which key is used for signing. However, it's being ignored.

What is being changed

If keyRef is supplied, it's used to select a specific key of the identifier. If it's not supplied, the uses the first key (current behavior).

Quality

Check all that apply:

• I want these changes to be integrated
• I successfully ran pnpm i, pnpm build, pnpm test, pnpm test:browser locally.
• I allow my PR to be updated by the reviewers (to speed up the review process).
• I added unit tests.
• I added integration tests.
• I did not add automated tests because _________, and I am aware that a PR without tests will likely get rejected.

[mirceanis]

looks good, kudos for updating the tests!

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (6981e68) 84.48% compared to head (178df94) 84.49%.

Additional details and impacted files

@@           Coverage Diff           @@
##             next    #1202   +/-   ##
=======================================
  Coverage   84.48%   84.49%           
=======================================
  Files         158      158           
  Lines       16625    16635   +10     
  Branches     1823     1826    +3     
=======================================
+ Hits        14046    14056   +10     
  Misses       2579     2579           

Impacted Files	Coverage Δ
packages/credential-w3c/src/action-handler.ts	81.90% <100.00%> (+0.35%)	⬆️

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.