Allow X or X% hosts to have bad values

Say we're measuring replication lag and we have `10` replicas. For some apps, it would be OK if one lags. Maybe two. And it would be better let them lag and have ongoing operations, as opposed to stalling everything.

The suggestion is to have a per-cluster config that indicates how many hosts can be down. This would either be an absolute number, or a ratio/percentile. For smaller setups it makes more sense to have an absolute number (e.g. "1 host can be lagging"). For larger setups it may be better to work by percentile ("up to 5% of hosts may be lagging").

I'm unsure whether to support both.

No files, tests, or entry points are named. Start by locating the per-cluster configuration and the replication-lag health or throttling logic, then determine whether absolute limits, percentage limits, or both are supported. Done should define the configuration behavior and allow the chosen number or proportion of lagging hosts without stalling ongoing operations.

Written by the indexing model from the issue text.