`emissions` : improve slashing

[kingpinXD]

• Slash by percentage instead of a fixed amount.
• Add a jailing or pausing mechanism for the observers in the observer set

[kingpinXD]

Adding some notes here

• Right not an observer can vote wrong on 49% of ballots in a block and still get rewarded for the 1% extra in the correct votes . https://github.com/zeta-chain/zeta-node/blob/14e7ebb19522c1207d229896300ca04c08404574/x/observer/types/ballot.go#L87-L107

This behavior should be changed to slashing for the block if one of the votes is wrong. However, this can only be added in after some kind of jailing or pausing mechanism is added so that it gives the observer an opportunity to check if there is something wrong with their zeta client configuration before unpausing ,