[StateAccumulatorV2] Enable on mainnet for next release (#18178)

## Description 

To be picked up in 1.29

## Test plan 

How did you test the new or updated feature?

---

## Release notes

Check each box that your changes affect. If none of the boxes relate to
your changes, release notes aren't required.

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that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:

crates/sui-core/src/authority/epoch_start_configuration.rs

@@ -86,8 +86,7 @@ impl EpochFlag {
 
         if enable_state_accumulator_v2 {
             new_flags.push(EpochFlag::StateAccumulatorV2EnabledTestnet);
-            // TODO: enable on mainnet
-            // new_flags.push(EpochFlag::StateAccumulatorV2EnabledMainnet);
+            new_flags.push(EpochFlag::StateAccumulatorV2EnabledMainnet);
         }
 
         new_flags