docs: add changelogs for 9974

changes/v5.0.18/fix-9974.en.md

@@ -0,0 +1,2 @@
+Report memory usage to statsd and prometheus using the same data source as dashboard.
+Prior to this fix, the memory usage data source was collected from an outdated source which did not work well in containers.

changes/v5.0.18/fix-9974.zh.md

@@ -0,0 +1,2 @@
+Statsd 和 prometheus 使用跟 Dashboard 相同的内存用量数据源。
+在此修复前，内存的总量和用量统计使用了过时的（在容器环境中不准确）的数据源。