Change the spartan bucket parameters in order to allow withdrawals to be back

Context

With the UST claims payouts, the spartan bucket is currently over used and therefore withdrawals are not possible unless more deposits are made or unless there are changes to the parameters. The spartan bucket derisking that started taking place earlier enables some small parameters change and would allow to have some free float ETH for the withdrawals to take place.

Proposal

1. Allow up to 1800 ETH of free float ETH to be available by updating the spartan bucket parameters to take into account the derisking that started taking place and by also taking into account the policies set to expire in the coming months.
2. Exchange to ETH enough stETH from asset management to make the withdrawals possible (estimate 1500 stETH).
3. I am comfortable with using boardroom (I think it was discussed here already) for onchain execution

With this change, after the 1800 ETH withdrawals, the premiums and rollovers will only move a little bit. stETH price variations however will continue to have an impact as it is the case already.