Added signing utilities for vc-jws, with the appropriate content type.

[andresuribe87]

This fixes #272

[codecov-commenter]

Codecov Report

Merging #273 (e10d309) into main (e1cd85d) will decrease coverage by 0.14%.
The diff coverage is 45.24%.

@@            Coverage Diff             @@
##             main     #273      +/-   ##
==========================================
- Coverage   60.48%   60.34%   -0.14%     
==========================================
  Files          39       40       +1     
  Lines        4398     4440      +42     
==========================================
+ Hits         2660     2679      +19     
- Misses       1311     1328      +17     
- Partials      427      433       +6     

Impacted Files	Coverage Δ
crypto/jwt.go	48.50% <0.00%> (-1.24%)	⬇️
credential/signing/jws.go	51.35% <51.35%> (ø)

[decentralgabe]

I like this, but I'm hesitant to start using it given it hasn't seen any consensus or adoption (yet) in the working group. I wonder if we could add a go build tag for "experimental" or similar.

[andresuribe87]

I wonder if we could add a go build tag for "experimental" or similar.

We could do this. A simpler approach would be to make that known in the godoc of the functions introduced. Thoughts?

[decentralgabe]

agree with that