Respect chain override in genesis system object generation (MystenLab…

…s#15632)

## Description 

As in title

## Test Plan 

Will check against CI test

---
If your changes are not user-facing and do not break anything, you can
skip the following section. Otherwise, please briefly describe what has
changed under the Release Notes section.

### Type of Change (Check all that apply)

- [ ] protocol change
- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes

crates/sui-genesis-builder/src/lib.rs

@@ -1013,12 +1013,9 @@ pub fn generate_genesis_system_object(
     token_distribution_schedule: &TokenDistributionSchedule,
     metrics: Arc<LimitsMetrics>,
 ) -> anyhow::Result<()> {
-    // We don't know the chain ID here since we haven't yet created the genesis checkpoint.
-    // However since we know there are no chain specific protocol config options in genesis,
-    // we use Chain::Unknown here.
     let protocol_config = ProtocolConfig::get_for_version(
         ProtocolVersion::new(genesis_chain_parameters.protocol_version),
-        sui_protocol_config::Chain::Unknown,
+        ChainIdentifier::default().chain(),
     );
 
     let pt = {

crates/sui-types/src/digests.rs

@@ -160,8 +160,8 @@ pub struct ChainIdentifier(CheckpointDigest);
 pub static MAINNET_CHAIN_IDENTIFIER: OnceCell<ChainIdentifier> = OnceCell::new();
 pub static TESTNET_CHAIN_IDENTIFIER: OnceCell<ChainIdentifier> = OnceCell::new();
 
-/// For testing purposes, you can set this environment variable to force protocol config to use
-/// a specific Chain.
+/// For testing purposes or bootstrapping regenesis chaing configuration, you can set
+/// this environment variable to force protocol config to use a specific Chain.
 const SUI_PROTOCOL_CONFIG_CHAIN_OVERRIDE_ENV_VAR_NAME: &str = "SUI_PROTOCOL_CONFIG_CHAIN_OVERRIDE";
 
 static SUI_PROTOCOL_CONFIG_CHAIN_OVERRIDE: Lazy<Option<Chain>> = Lazy::new(|| {