Improvement: Simplify Rollup FP Configuration by Reducing Redundant Sections

## Description

When `ChainType = OPStackL2`, the config requires both `[babylon]` and `[opstackl2]` sections with mostly duplicated parameters (Key, ChainID, RPCAddr, etc.), causing confusion and potential misconfiguration. Even though `[opstackl2]` has Babylon RPC access, `[babylon] `section is still mandatory.