Disambiguate DRep being a key or a script in certificate descriptions

[smelc]

Changelog

- description: |
    Disambiguate DRep being a key or a script in certificate descriptions
# 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
  # - refactoring    # QoL changes
  # - 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 #756

How to trust this PR

Try the following before and after the PR:

# before
> cabal run cardano-cli -- conway governance drep registration-certificate   --drep-script-hash 8f33600845940d65bdbc7ea7a247a7997aa8558649128fa82c4c0468   --key-reg-deposit-amt "10000"   --out-file drep-multisig-reg.cert; cat drep-multisig-reg.cert | jq ".description"
"DRep Key Registration Certificate"

# after
> cabal run cardano-cli -- conway governance drep registration-certificate   --drep-script-hash 8f33600845940d65bdbc7ea7a247a7997aa8558649128fa82c4c0468   --key-reg-deposit-amt "10000"   --out-file drep-multisig-reg.cert; cat drep-multisig-reg.cert | jq ".description"
"DRep Script Registration Certificate"

and look at the diff of golden files

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• Self-reviewed the diff

[smelc]

cc @CarlosLopezDeLara, because I decided to go beyond #756 and change the labels for of retirement certificates and update certificates too, to be consistent.