Accept consistently dash-separated args in ccf_cose_sign1

[eddyashton]

Whenever using ccf_cose_sign1 by hand, we previously had to parse errors like:

$ ccf_cose_sign1 --content ./trigger_ledger_chunk_proposal.json --signing-cert member0_cert.pem --ccf-gov-msg-type proposal --ccf-gov-msg-created-at $(date -Is) --signing-key member0_privk.pem 
usage: ccf_cose_sign1 [-h] --content CONTENT --signing-cert SIGNING_CERT --ccf-gov-msg-type
                      {proposal,ack,state_digest,recovery_share,encrypted_recovery_share,ballot,withdrawal}
                      [--ccf-gov-msg-proposal_id CCF_GOV_MSG_PROPOSAL_ID] --ccf-gov-msg-created_at
                      CCF_GOV_MSG_CREATED_AT --signing-key SIGNING_KEY
ccf_cose_sign1: error: the following arguments are required: --ccf-gov-msg-created_at

To eventually realise that --ccf-gov-msg-created-at != --ccf-gov-msg-created_at, because the tool expects the final separator to be an underscore, not a dash. All because the eventual protected header is ccf.gov.msg.created_at. I think this is unhelpful, and there's no reason to expose this detail at the CLI level.

This change accepts both formats for this arg, so we lose no backwards compatibility but going forwards the tool is more likely to work first-time.

[achamayou]

Longer term I think we could and should switch to the SCITT format, with a CWT_Claims, and use iss instead of member id and iat instead of created_at, and sub instead of proposal_id.