Keep GenesisConfig binary compatible with v0.23 (#8617)

automerge

(cherry picked from commit d3b458d)

sdk/src/genesis_config.rs

@@ -48,6 +48,9 @@ pub struct GenesisConfig {
     pub slots_per_segment: u64,
     /// network speed configuration
     pub poh_config: PohConfig,
+    /// this field exists only to ensure that the binary layout of GenesisConfig remains compatible
+    /// with the Solana v0.23 release line
+    pub __backwards_compat_with_v0_23: u64,
     /// transaction fee config
     pub fee_rate_governor: FeeRateGovernor,
     /// rent config
@@ -89,6 +92,7 @@ impl Default for GenesisConfig {
             slots_per_segment: DEFAULT_SLOTS_PER_SEGMENT,
             poh_config: PohConfig::default(),
             inflation: Inflation::default(),
+            __backwards_compat_with_v0_23: 0,
             fee_rate_governor: FeeRateGovernor::default(),
             rent: Rent::default(),
             epoch_schedule: EpochSchedule::default(),