Add JSON schema checking functionality for DRep and Gov action metadata

[palas]

Changelog

- description: |
    Added schema checking functionality for DRep registration, DRep update, and GovAction metadata, based on CIP-0100, CIP-0108, and CIP-0119. Updated tests. Refactored test data for improved code clarity.
  type:
  - feature
  - refactoring
  - test

Context

The objective is addressing this issue: #906

This PR is based on cardano-api PR #713, which provides the required functionality, and this PR should not be merged until the cardano-api PR gets released and the source repo stanza is removed.

How to trust this PR

I think, checking the changes to the tests here is key, and the main part. The actual functionality is in cardano-api PR #713 (I would check that one together with this). The latest commit should also be pure refactoring.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff

[gitmachtl]

I just took a look at the testfiles and i noticed the one which has the authors signed with method "cip-0008".

The signature provided in this example is the COSE_SIGN1, ok. But the publicKey is not really the COSE_KEY, its only the public key. As CIP-0008 supports actually different methods, do we simply demand that the

COSE_Key map label '1' (kty) is '1' (OKP)
COSE_Key map label '3' (alg) is '-8' (EdDSA)
COSE_Key map label '-1' (crv) is '6' (Ed25519)

?

If so, is this written somewhere in the CIP-100 (and dependencies) ?

Or should in the case of using method "cip-0008" the publickey actually be the COSE_Key ?

@Ryun1 @CarlosLopezDeLara