chore(openapi): prepare removal of signer_registration_protocol and cardano_transactions_signing_config from EpochSettingsMessage

- mark both fields as deprecated
- make `signer_registration_protocol` optional

Author: Alenar

openapi.yaml

@@ -995,11 +995,11 @@ components:
         - epoch
         - current_signers
         - next_signers
-        - signer_registration_protocol
       properties:
         epoch:
           $ref: "#/components/schemas/Epoch"
         signer_registration_protocol:
+          deprecated: true
           $ref: "#/components/schemas/ProtocolParameters"
         current_signers:
           type: array
@@ -1010,6 +1010,7 @@ components:
           items:
             $ref: "#/components/schemas/Signer"
         cardano_transactions_signing_config:
+          deprecated: true
           $ref: "#/components/schemas/CardanoTransactionsSigningConfig"
       examples:
         - {