Update release notes (#3068)

* Update release notes

* add imdg version to release notes

Author: Ali

hazelcast-jet-distribution/src/root/release_notes.txt

@@ -46,6 +46,19 @@ Thank you for your valuable contributions!
 
 <<< END TEMPLATE FOR THE NEXT VERSION
 
+** Hazelcast Jet 4.5.1 **
+
+Hazelcast Jet 4.5.1 is based on IMDG version 4.2.2 .
+
+1. Fixes
+
+[core] Fix rebalance() nonfunctional before fused stages (#3051)
+[hadoop] Update Apache Commons Compress to 1.21
+[hadoop] Update JSON Small and Fast Parser to 2.4.7
+[hadoop] Update Jetty to 9.4.43
+[hadoop] Apache Commons IO to 2.7
+[metrics] Update Prometheus JMX Exporter - Java Agent to 0.16.1
+[elasticsearch] Update Elasticsearch6 to 6.8.17
 
 ** Hazelcast Jet 4.5 **