fyToken as collateral Wand

[alcueca]

Enabling fyToken as collateral is likely to follow a very similar pattern to fCash as collateral, including a new Join for each series. This will add additional work to each roll, which we would really like to avoid.

The solution can be to code a fyToken Wand, that allows to add any existing fyToken as collateral to borrow its underlying.

Some features that would be required:

• Factory pattern to deploy the needed Join within the governance transaction. We can use CREATE2 as long as the Timelock gets exclusive ROOT access (for example by hardcoding it in the bytecode). We could be attacked by DoS, but as long as we keep control that would be an acceptable risk.
• All fyToken in the Cauldron accepted as collateral for their underlying, with a governance-set mapping of forbidden series or underlyings.
• Automated configuration of Ladle, Oracles, Witch and Cauldron.