New “transactionValidation” graphql subscription API

[Chralu]

Describe the solution you'd like

This subscription should replace both transactionConfirmed(address: Address!): TransactionAttestation and transactionError(address: Address!): TransactionError.

transactionValidation sends notification when transaction validation is done (either on a failure or success).

/// On success
{
  address: Address,
  success: {
    crossValidationStamps: [
      {
          nodePublicKey: PublicKey,
          signature: Hex
      },
    ],
  },
}

/// On Failure
{
  address: Address,
  failure: {
    context: ErrorContext,
    error: ErrorDetails
  }
}