Add ubuntu 26 support (#2219)

Co-authored-by: Kidus Asrade <kidusasr@amazon.com>

Author: kidmun

tool/clean/clean_ami/clean_ami.go

@@ -42,6 +42,7 @@ var imagePrefixes = []string{
 	"cloudwatch-agent-integration-test-ubuntu-24",
 	"cloudwatch-agent-integration-test-ubuntu-LTS-22",
 	"cloudwatch-agent-integration-test-ubuntu-25",
+	"cloudwatch-agent-integration-test-ubuntu-26",
 	"cloudwatch-agent-integration-test-win-10",
 	"cloudwatch-agent-integration-test-win-11",
 	"cloudwatch-agent-integration-test-win-2016",