Add --staking flag (#1641)

## Issue Addressed

Closes #1472 

## Proposed Changes

Add `--staking` ~~and`staking-with-eth1-endpoint`~~ flag to improve UX for stakers.


Co-authored-by: Paul Hauner <paul@paulhauner.com>

beacon_node/eth1/src/http.rs

@@ -55,6 +55,19 @@ impl FromStr for Eth1NetworkId {
     }
 }
 
+/// Checks that the provided eth1 node has all the relevant api endpoints open
+/// and returns the network id.
+pub async fn check_eth1_endpoint(
+    endpoint: &str,
+    timeout: Duration,
+) -> Result<Eth1NetworkId, String> {
+    // Checks that the "eth" api works as expected.
+    let _block_number = get_block_number(endpoint, timeout).await?;
+    // Checks that the "net" api works as expected.
+    let network_id = get_network_id(endpoint, timeout).await?;
+    Ok(network_id)
+}
+
 /// Get the eth1 network id of the given endpoint.
 pub async fn get_network_id(endpoint: &str, timeout: Duration) -> Result<Eth1NetworkId, String> {
     let response_body = send_rpc_request(endpoint, "net_version", json!([]), timeout).await?;