Isthmus: L2 Genesis Simplification

[skeletor-spaceman]

The spec for this is defined in ethereum-optimism/specs#358

The rationale is in ethereum-optimism/specs#350

[tynes]

This doesn't necessarily need to be tied to the interop release itself and is related to ongoing holocene hardfork work in ethereum-optimism/specs#340. A lot of projects all need this generic L1 -> L2 config setter logic

[BlocksOnAChain]

FYI: I'm Changing the priority on this issue to P2(Optional for the Holocene release), as instructed by @sebastianst on our last weekly sync for Holocene.

[BlocksOnAChain]

I will remove this item from the scope for Holocene, based on what @tynes shared on it:
"I would like to cut Standard L2 Genesis from scope. This would delay the release of holocene.
There will be another fork after Holocene that includes the Standard L2 Genesis"