RBAC registration Proposer (Role 3) validation

[bkioshn]

Summary

RBAC registration Proposer (Role 3) validation

Description

Add validation for Role 3 Proposer according to the specification.

1. The proposer must define an ED25519 public key as their signature key, and it must be the second key (index 1) in the list of simple public keys (pub-keys). This key will be used for signing proposals or transactions.
2. Optional encryption key : but if defined must be a reference to the second or third key in the simple key array.
3. If the proposers registration does not define a payment key, the Role 0 payment key is used for the proposers payment key.

https://github.com/input-output-hk/catalyst-CIPs/tree/x509-catalyst-role-definitions/CIP-XXXX#proposer-registration

[bkioshn]

Closing this issue since came into a conclusion that there should not be other strict requirement for non-role 0 except for role 0 index cert and public key which is already implemented