CLI: Support retrieving past leader schedules (bp #14304) (#14311)

* clap-utils: Add epoch validator

(cherry picked from commit a709850ee4)

* CLI: Support displaying past leader schedules

(cherry picked from commit bd761e2a52)

Co-authored-by: Trent Nelson <trent@solana.com>

clap-utils/src/input_validators.rs

@@ -1,7 +1,7 @@
 use crate::keypair::{parse_keypair_path, KeypairUrl, ASK_KEYWORD};
 use chrono::DateTime;
 use solana_sdk::{
-    clock::Slot,
+    clock::{Epoch, Slot},
     hash::Hash,
     pubkey::Pubkey,
     signature::{read_keypair_file, Signature},
@@ -148,6 +148,13 @@ where
     }
 }
 
+pub fn is_epoch<T>(epoch: T) -> Result<(), String>
+where
+    T: AsRef<str> + Display,
+{
+    is_parsable_generic::<Epoch, _>(epoch)
+}
+
 pub fn is_slot<T>(slot: T) -> Result<(), String>
 where
     T: AsRef<str> + Display,