[Improvement] Add indicators to judge whether the node is healthy

At present, there is only disk i/o in the health detection of the machine. Whether to add the index of memory utilization? What do u think of that? @jerqi

Start by tracing the existing disk I/O health detection described in the issue and identify the node-health entry point and its tests. Determine how memory utilization should be measured and judged alongside disk I/O; done means the health detection reports the memory indicator consistently and its behavior is covered by tests.

Written by the indexing model from the issue text.