Fix key type issue

[andresuribe87]

This PR exposes the key type used when decoding the DIDKey. This is needed as otherwise the information would be lost when decoding.

This is a prerequisite to fixing TBD54566975/ssi-service#181.

Note that I had to update some examples of the tests, since the test vectors appear to have been incorrectly generated.

[decentralgabe]

Looks good but may be cleaner as a new receiver method on DIDKey that is just GetKeyType

[codecov-commenter]

Codecov Report

Merging #255 (cf4dd5f) into main (ecc1264) will increase coverage by 0.10%.
The diff coverage is 61.76%.

@@            Coverage Diff             @@
##             main     #255      +/-   ##
==========================================
+ Coverage   59.03%   59.13%   +0.10%     
==========================================
  Files          38       38              
  Lines        4459     4490      +31     
==========================================
+ Hits         2632     2655      +23     
- Misses       1407     1410       +3     
- Partials      420      425       +5     

Impacted Files	Coverage Δ
did/util.go	51.58% <30.77%> (+1.58%)	⬆️
did/key.go	65.73% <67.31%> (+0.36%)	⬆️
did/peer.go	65.37% <100.00%> (ø)
did/web.go	68.42% <100.00%> (ø)