Rollup node: fix l1_monitor_finalized being ignored from config file

What

This merge request addresses an issue where the l1_monitor_finalized configuration setting for the rollup node was being ignored. Previously, changes to this setting in the configuration file were not correctly applied, leading to unintended behavior in how the rollup node monitored finalized L1 blocks.

Why

The l1_monitor_finalized setting was being overridden by the CLI argument even when it as not present.

How

The fix involves modifying the rollup node's configuration loading mechanism to correctly apply the l1_monitor_finalized value from the configuration file as a default when the flag --l1-monitor-finalized is not present. This ensures that the setting is no longer overlooked and is properly integrated into the node's operational parameters.