Hardfork validation needs to be adapted when we make chain types extensible

[schaable]

Current behavior: the hardfork value in the user config is validated by Zod as a value in the HardforkName enum. However, this validation is only appropriate for the l1 chain type.

Expected behavior: the hardfork validation should either be based on the chainType or skipped entirely.

[schaable]

This issue should take the overrides into account.