add hardcoded chain spec: shell_kusama_lease2

[clangenb]

This will be the chain-spec that we register for the next slot.

[brenzi]

Once we hand over this slot to our main parachain, the genesis shell_kusama_lease2will not be necessary anymore. There is no strict need for hardcoding this into our binaries as we ourselves will be the only ones running nodes (if necessary at all), so a json spec would do too. So I even think you don't need an extra release of our parachain for this

[clangenb]

I agree that this will not be necessary in the future and that a plain json is enough. I just want to be as explicit as possible to minimize the chances of a genesis mismatch. Would you suggest that plain wiki documentation is enough?