Update function `registerValidator` to add `proof` parameter

[cmjc]

PR https://github.com/clearmatics/autonity-internal/pull/180 in the development repo is modifying the existing functionality for validator registration to verify the submitter is the validator operator by generating a proof using the validator's private node key:

• modifying the registerValidator function to add a proof parameter

• adding a new command in the autonity binary to generate the proof:

  ./autonity genEnodeProof --nodekey <nodekeyFile> <treasuryAddress>

This will require update to the existing autcli function register in the aut validator function grouping.

Tasks:

• [ ] update aut validator register to:
  • [ ] add proof parameter.
  • [ ] call genEnodeProof to generate proof with necessary params.