feat (vpool): allow for random vpool parameters in simulation

[matthiasmatt]

The parameters for the vpool should be randomized within safe values.
It can be done, but random transactions from the perp simulation will need to mathematically guarantee that all operations in x/perps will pass with random values of TradeLimitRatio, FluctuationLimitRatio, and MaxLeverage.

Some modules in the cosmos-sdk (e.g. x/bank) first simulate the tx and only if it passes, uses the message as the operation. We should implement this approach.