Updating Release Notes for 1.300065.0 (#2055)

Author: sky333999

RELEASE_NOTES

@@ -1,3 +1,15 @@
+========================================================================
+Amazon CloudWatch Agent 1.300065.0 (2026-03-17)
+========================================================================
+Features:
+* [Agent] Add pipeline for system metrics on recognized hosts
+
+Enhancements:
+* [Collectd] Adds append_dimensions to collectd, supporting custom metric dimensions
+
+Bug Fixes:
+* [Agent] Handle regex escaping for '+' in timestamp format
+
 ========================================================================
 Amazon CloudWatch Agent 1.300064.1 (2026-02-05)
 ========================================================================