Allow for registration of DRep scripts

[carlhammann]

Changelog

- description: |
     - add support for registration of script DReps;
     - rework the `conway governance hash` command: separate sub-commands for anchor data and scripts
# 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

This PR closes #559. The issue proposes adding a --script-hash and a --script-file flag to the conway governance drep registration-certificate command. In the spirit of #442, I choose to implement only one of these flags, as --drep-script-hash, and instead add a new sub-command to the conway governance hash command, to enable computation of script hashes. This is done in bf65a3a.

How to trust this PR

Highlight important bits of the PR that will make the review faster. If there are commands the reviewer can run to observe the new behavior, describe them.

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

[smelc]

Nice design ❤️

[carbolymer]

ProposalText for binary files is quite misleading here. We should use use a different type here. Not necessarily within the scope of this PR.

[carlhammann]

I opened an issue for that: #568