Governance metadata is not validated

[saratomaz]

Description

There is no metadata validation for the governance metadata. Right now is possible to submit a governance action with wrong metadata/missing required fields and the only time we can see an error is when dbsync try to catch the data.

Steps to Reproduce

e.g.

1. run cardano-cli conway governance drep metadata-hash --drep-metadata-file drep_metadata.json
   drep_metadata.json -> missing givenName that is marked as Compulsory in cip-0119
2. No error is returned

Additional Context

CIPs related to governance metadata:
https://github.com/cardano-foundation/CIPs/tree/master/CIP-0100
https://github.com/cardano-foundation/CIPs/tree/master/CIP-0108
https://github.com/cardano-foundation/CIPs/tree/master/CIP-0119

[kderme]

In case cli plans to support this, we have implemented metadata parsers following the above cips https://github.com/IntersectMBO/cardano-db-sync/blob/master/cardano-db-sync/src/Cardano/DbSync/OffChain/Vote/Types.hs

[gitmachtl]

cardano-signer is doing checks if a metadata file is valid, also checks about the signatures.