correct heartbeat timeout to distributor lifecycler for ring page (#7253)

Passes the correct `heartbeat_timeout` to the created lifecycler config
in distributor ring construction. When we didn't include this, it would
create a visual bug incorrectly marking many distributors as unhealthy
when in fact they were in fine condition. Including

The _lifecycler_ `heartbeat_timeout` is _only_ referenced in the status
page
[here](74c8cf03ba/vendor/github.com/grafana/dskit/ring/lifecycler.go (L892-L894)).
The _ring_ `heartbeat_timeout` continues to be updated correctly.

pkg/distributor/distributor_ring.go

@@ -79,6 +79,7 @@ func (cfg *RingConfig) ToLifecyclerConfig() ring.LifecyclerConfig {
 	lc.InfNames = cfg.InstanceInterfaceNames
 	lc.UnregisterOnShutdown = true
 	lc.HeartbeatPeriod = cfg.HeartbeatPeriod
+	lc.HeartbeatTimeout = cfg.HeartbeatTimeout
 	lc.ObservePeriod = 0
 	lc.NumTokens = 1
 	lc.JoinAfter = 0