Proposer preparation data quoted validator index in API
## Issue Addressed
## Proposed Changes
Quotes around validator index in `prepare_beacon_proposer` endpoint
@@ -6,6 +6,7 @@ use serde::{Deserialize, Serialize};
#[derive(PartialEq, Debug, Serialize, Deserialize, Clone)]
pub struct ProposerPreparationData {
/// The validators index.
+ #[serde(with = "eth2_serde_utils::quoted_u64")]
pub validator_index: u64,
/// The fee-recipient address.
pub fee_recipient: Address,
