Strengthen warning about JVM agents (elastic#2068)

It's not just about performance and they don't just cause nodes to crash
or freeze, the problems might be stability or corruption too. This
commit makes the warning in the docs more expansive.

Co-authored-by: David Kilfoyle <[email protected]>

Author: DaveCTurner

deploy-manage/deploy/self-managed/installing-elasticsearch.md

@@ -108,7 +108,7 @@ If you decide to run {{es}} using a version of Java that is different from the b
 To use your own version of Java, set the `ES_JAVA_HOME` environment variable to the path to your own JVM installation. The bundled JVM is located within the `jdk` subdirectory of the {{es}} home directory. You may remove this directory if using your own JVM.
 
 :::{warning}
-Don’t use third-party Java agents that attach to the JVM. These agents can reduce {{es}} performance, including freezing or crashing nodes.
+Don’t use third-party Java agents that attach to the JVM. Such agents can be harmful to {{es}} stability and performance. In some cases they may cause nodes to freeze, crash, or fail to start up, or to lose or corrupt your data.
 :::
 
 ## Third-party dependencies [dependencies-versions]