Update cloudfoundry for 1.28.4 release

Author: jackshirazi

cloudfoundry/index.yml

@@ -34,3 +34,4 @@
 1.28.1: https://repo1.maven.org/maven2/co/elastic/apm/elastic-apm-agent/1.28.1/elastic-apm-agent-1.28.1.jar
 1.28.2: https://repo1.maven.org/maven2/co/elastic/apm/elastic-apm-agent/1.28.2/elastic-apm-agent-1.28.2.jar
 1.28.3: https://repo1.maven.org/maven2/co/elastic/apm/elastic-apm-agent/1.28.3/elastic-apm-agent-1.28.3.jar
+1.28.4: https://repo1.maven.org/maven2/co/elastic/apm/elastic-apm-agent/1.28.4/elastic-apm-agent-1.28.4.jar