refactor(zk_toolbox): Minimize dependency on zksync_config

[slowli]

What ❔

Largely removes zkstack dependency on zksync_config.

Why ❔

This dependency significantly complicates new config system integration. While the alternative is less typesafe, it can be made more typesafe in the future once the config system integration is complete (a node binary can then be used to validate the changed config values).

Checklist

• PR title corresponds to the body of PR (we generate changelog entries from PRs).
• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• Code has been formatted via zkstack dev fmt and zkstack dev lint.

[slowli]

The remaining zksync_config uses in the config crate are related to GatewayConfig and GatewayChainConfig. Not sure what to do with these mentions because both configs are created from scratch in migrate_from_gateway / migrate_to_gateway modules (rather than being created from a template); so using the same approach as for GeneralConfig etc. is somewhat problematic. OTOH, these configs do not adhere to Protobuf serialization format anyway 🤷 I guess they could be dealt with in a separate PR (still before the config system integration).

[popzxc]

Yes! Nice!

I'd still recommend getting a review from @sanekmelnikov before merging.

[slowli]

@sanekmelnikov JFYI, I've decided to not add stronger-typed config wrappers to zkstack in this PR because it'd make this PR unreasonably large. (E.g., some follow-up changes that I have stashed remove api.web3_json_rpc.http_url and other params not read by the server.)