Attestation (-a) can result in duplicate signatures

[catch-21]

When signing all metadata for a second time then duplicate keys are included in metadata json. It would be more user friendly if it overwrote existing signatures.

For example

• Metadata json has already been created and signed for: name and description.
• I correct a typo in the name be re-run cardano-metadata-submitter <subject> --name "Jamescoin" (signature has been correctly removed from metadata json)
• I re-run attestation for whole metadata cardano-metadata-submitter <subject> -a policy.skey

Actual Result

Metadata json has duplicate signatures for description.

Expected Result

No duplicates, only one signature entry per pubkey.

Notes

It is possible to specify --attest-name to prevent the duplication of description signatures in the above scenario, but it would still be good to validate and prevent duplicates from being possible.

[catch-21]

https://github.com/cardano-foundation/cardano-token-registry/wiki/How-do-I-update-my-entry-in-the-registry%3F This page in the token registry wiki actually says "Produce new signatures using cardano-metadata-submitter that will replace the existing ones", just incase this bumped priority here.