Figure out if there is a way to sign attestations with consensus key

[gjermundgaraba]

Right now attestations are signed in the sidecar with a key that is separate from the validators consensus key. It would be nice if there was a way to move this to the abci implementation and instead use the validators own consensus key.

The reason this would be useful is because currently we need to have a registry (in the configmodule) that maps a validator to the attester id and public key.

If the attestation was instead signed with the consensus key, we could look up the validator directly with the public key and verify the signature directly, with no extra registry step involved.

I currently believe this would need to go through some kind of API in cometBFT, because the validator key is not guaranteed to be available on the machine itself (when using a remote signer).