[Docs] Custom S3 CA must be reinstalled on upgrade (elastic#103168) (e…

…lastic#103249)

This commit updates the docs to call out that custom certificate
authorities for S3 repositories will need to be reinstalled every time
ES is upgraded, is the node is using the bundled JDK

docs/reference/snapshot-restore/repository-s3.asciidoc

@@ -123,7 +123,9 @@ settings belong in the `elasticsearch.yml` file.
     `https`. Defaults to `https`. When using HTTPS, this repository type validates the
     repository's certificate chain using the JVM-wide truststore. Ensure that
     the root certificate authority is in this truststore using the JVM's
-    `keytool` tool.
+    `keytool` tool. If you have a custom certificate authority for your S3 repository
+    and you use the {es} <<jvm-version,bundled JDK>>, then you will need to reinstall your
+    CA certificate every time you upgrade {es}.
 
 `proxy.host`::