Create StakePoolState

[lehins]

Today we use PoolParams as the state as well as information for registering and updating a stake pool.
There is a limitation of this approach, since we will soon need to add other things to the stake pool state. We also don't need to keep PoolId in both the state and the key of PState and we need to move the deposit into the state

This task tracks creation of an era parametric StakePoolState data type. If we ever need to convert it later to a type family, we will, but for now, I think it sufficient to convert it to a regular data type

This ticket is blocked by #4694