/eth/v1/node/syncing endpoint does not return correct output as per beacon spec

[nidhi-singh02]

The beacon API spec returns the output below

{
  "data": {
    "head_slot": "1",
    "sync_distance": "1",
    "is_syncing": true,
    "is_optimistic": true,
    "el_offline": true
  }
}

However the node syncing endpoint in here returns *api.Response[*apiv1.SyncState] and this is how SyncState looks like- it is missing field el_offline.

// SyncState is the data regarding the node's synchronization state to the chain.
type SyncState struct {
	// HeadSlot is the head slot of the chain as understood by the node.
	HeadSlot phase0.Slot
	// SyncDistance is the distance between the node's highest synced slot and the head slot.
	SyncDistance phase0.Slot
	// IsOptimistic is true if the node is optimistic.
	IsOptimistic bool
	// IsSyncing is true if the node is syncing.
	IsSyncing bool
}

I am happy to raise a PR to fix this.