Incumbent bonus on multisig set

[davidsiska-vega]

We have incumbent bonus on tendermint / consensus set to avoid excessive flipping of validators caused by small change in stake.

We need the same mechanism for multisig set (can use the same parameter network.validators.incumbentBonus or it can have its own netparam e.g. network.validators.multisigIncumbentBonus.

Basically, we penalise validators if the “multisig set” (which currently is the top n) is different to what the signers are on ethereum. The idea of this change would be that the “multisig set” will no longer be the top n but there will be an incumbent bonus preventing the (n+1)-st validator entering the multisig set unless the difference in score / stake (can’t remember which we use but we want to use whatever is used now) is big enough.