Investigate slashing as an extension

[minghinmatthewlam]

Context and scope
For ValidatorManager contract we don't have the concept of slashing, and rely on validators to be incentivized by getting their initial stake amount back + possible rewards, but L1s might look to add slashing for additional effects for misperforming validators.

Discussion and alternatives
Is slashing needed, or is the validator's initial stake enough incentive? How does slashing a validator affect the delegation rewards? Negative rewards calculated from the reward manager seems like an easy example, but are there more considerations there.