Stop hardcoding EIP1559Elasticity (and store in the registry)

[geoknee]

Chains which use a value other than 6 will fail the automated checks in add-chain and cannot be added to the registry (at present).

op-geth function which defaults this to 6:

https://github.com/ethereum-optimism/op-geth/blob/0f5b9dcfd2ac66f6fd8faae526b1549721f5f392/params/superchain.go#L78-L81

op-node function which defaults to 10 but allows the deploy config to override it:

https://github.com/ethereum-optimism/optimism/blob/2d32f8bfea15ad131bc7b98f732886b5bb9dcff6/op-chain-ops/genesis/genesis.go#L38-L41