feat: Limit the number of orders in merged solutions

[sunce86]

Problem

Sometimes merged solutions are too big (contain too many orders) and are hard to settle onchain since the probability of state changing in between the solving and settling time is high. We need some additional way to lower the chances of revert.

Suggested solution

Add a configuration parameter to driver that limits the number of orders per merged solutions.

[fleupold]

Basically we need to turn this constant into a config param.

[sunce86]

I think that constant limits the number of "mergings" to do, while we want to limit the number of orders per merged solution.