[#1367] writecache: Add background flushing objects limiter

To limit memory usage by background flush.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/writecache/cache.go

@@ -68,6 +68,7 @@ func New(opts ...Option) Cache {
 			maxBatchSize:    bbolt.DefaultMaxBatchSize,
 			maxBatchDelay:   bbolt.DefaultMaxBatchDelay,
 			metrics:         DefaultMetrics(),
+			flushSizeLimit:  defaultFlushWorkersCount * defaultMaxObjectSize,
 		},
 	}