[BUG] ResourceMonitor Incorrectly Triggers Unhealthy Status Despite Recyclable Memory

[qianheng-aws]

sql/opensearch/src/main/java/org/opensearch/sql/opensearch/monitor/OpenSearchMemoryHealthy.java

Lines 53 to 58 in 7892b90

	static class MemoryUsage {
	public long usage() {
	final long freeMemory = Runtime.getRuntime().freeMemory();
	final long totalMemory = Runtime.getRuntime().totalMemory();
	return totalMemory - freeMemory;
	}

ResourceMonitor get the memory usage by using total memory - free memory. While the whole process of a query(even other queries previous to the current one) will accumulate the memory usage until GC.

Originally posted by @qianheng-aws in #3971 (comment)

[LantaoJin]

resolved by #3983