verification-key: support DRep keys as well as committee keys, extended or not

[smelc]

Changelog

- description: |
    verification-key: support DRep keys as well as committee keys, extended or not
# uncomment types applicable to the change:
  type:
  - feature        # introduces a new feature
  # - breaking       # the API has changed in a breaking way
  - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - improvement    # QoL changes e.g. refactoring
  - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

Context

Fixes https://github.com/IntersectMBO/cardano-cli/issues/651

How to trust this PR

• Run the new tests before the PR, witness the tests don't pass
• Run the new tests on the PR's head, witness the tests pass

Checklist

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