Maximum number of active validators at any moment.
We do not allow the number of validators in any epoch to go above this.
Lower-bound on the amount of stake required to become a validator.
A validator can have stake below validator_low_stake_threshold
for this many epochs before being kicked out.
Validators with stake amount below validator_low_stake_threshold are considered to
have low stake and will be escorted out of the validator set after being below this
threshold for more than validator_low_stake_grace_period number of epochs.
Validators with stake below validator_very_low_stake_threshold will be removed
immediately at epoch change, no grace period.