Support forking outside the OP Stack

[fainashalts]

Devs building multichain applications may want to test chains outside of the Superchain, and we should enable this in a way that is least disruptive to the Supersim development flow. By default, Supersim should still check the Superchain registry for chain information. But we should also allow devs to specify custom forks.

If we offer a config for devs to add chain information for chains they want to test with, orchestrator can check there for an indicated chain name for forking. It should look something like:

"arbitrum": {
    "url": <<rpc url>>, 
    "blockNumber": <<block number for forking>>
}

If a developer is using a chain outside the registry, we should not kick off any of the OP-related predeploys or simulation.

[tabshaikh]

I would like to take this up and push it to another notch to have polymer labs integration that interacts with different L2 clusters