op-reth: Provide all command-line args as environment variables

We should make sure that all command-line options can also be set using environment variables.

This improves dev-ops ergonomics and avoids the need for ad-hoc scripts to translate environment variables to command-line options.

Based on this comments https://github.com/ethereum-optimism/optimism/pull/21551#discussion_r3543956313 and previous discussions with @yashvardhan-kukreja and @geoknee.

Start by locating op-reth's command-line parsing entry point and inventory every option. Then trace how configuration is loaded and determine the environment-variable naming convention. Done means all command-line options have equivalent environment-variable inputs, with coverage confirming both paths behave consistently.

Written by the indexing model from the issue text.