Add interfaces requested for `spells-mainnet`

[riccardopersiani]

Code: dss-interfaces: https://github.com/sky-ecosystem/spells-mainnet/blob/master/src/DssSpell.t.base.sol

// TODO: add full interfaces to dss-interfaces and remove from here
interface FlapUniV2Like {

// TODO: add full interfaces to dss-interfaces and remove from here
interface SplitLike {

// TODO: add full interfaces to dss-interfaces and remove from here
interface UsdsJoinLike is DaiJoinAbstract {}