fix: revert using agg mode by default (#1738)

Closes #1736 

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
- Introduced a default setting for the aggregator, making
`nodeConfig.Aggregator` true by default if the `"rollkit.aggregator"`
flag is not specified. This simplifies the configuration process for
users.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: yarikbratashchuk

cmd/rollkit/commands/run_node.go

@@ -58,6 +58,11 @@ func NewRunNodeCmd() *cobra.Command {
 				return err
 			}
 
+			// use aggregator by default
+			if !cmd.Flags().Lookup("rollkit.aggregator").Changed {
+				nodeConfig.Aggregator = true
+			}
+
 			// Update log format if the flag is set
 			if config.LogFormat == cometconf.LogFormatJSON {
 				logger = cometlog.NewTMJSONLogger(cometlog.NewSyncWriter(os.Stdout))