Add MINIMUM_STAKE_DELEGATION constant (#23259)

Co-authored-by: Tyera Eulberg <teulberg@gmail.com>

sdk/program/src/stake/mod.rs

@@ -5,3 +5,8 @@ pub mod state;
 pub mod program {
     crate::declare_id!("Stake11111111111111111111111111111111111111");
 }
+
+/// The minimum stake amount that can be delegated, in lamports.
+/// NOTE: This is also used to calculate the minimum balance of a stake account, which is the
+/// rent exempt reserve _plus_ the minimum stake delegation.
+pub const MINIMUM_STAKE_DELEGATION: u64 = 1;