DRep retirement-certificate support for script based DReps

[CarlosLopezDeLara]

#What

As a script-based DRep (i.e. multisig) I want to be able to generate a retirement (unregister) certificate, compliant with the conway cddl

unreg_drep_cert = (17, drep_credential, coin)

credential =
  [  0, addr_keyhash
  // 1, scripthash
  ]

So we need to expand drep retirement-certificate so that it can also take a scripthash, i.e.

cardano-cli conway governance drep retirement-certificate
                                                                   ( --drep-verification-key STRING
                                                                   | --drep-verification-key-file FILE
                                                                   | --drep-key-hash HASH
                                                                   | --drep-script-hash HASH
                                                                   )
                                                                   --deposit-amt LOVELACE
                                                                   --out-file FILE

[palas]

Closed by #678