OBSDOCS-794: Add known Splunk log forwarding issue to 5.8 release notes

Author: abrennan89

modules/logging-release-notes-5-8-0.adoc

@@ -56,6 +56,10 @@ In order to support multi-cluster log forwarding in additional namespaces other
 [id="logging-release-notes-5-8-0-known-issues"]
 == Known Issues
 
+* Currently, Splunk log forwarding might not work after upgrading to version 5.8 of the {clo}. This issue is caused by transitioning from OpenSSL version 1.1.1 to version 3.0.7. In the newer OpenSSL version, there is a default behavior change, where connections to TLS 1.2 endpoints are rejected if they do not expose the link:https://datatracker.ietf.org/doc/html/rfc5746[RFC 5746] extension.
++
+As a workaround, enable TLS 1.3 support on the TLS terminating load balancer in front of the Splunk HEC (HTTP Event Collector) endpoint. Splunk is a third-party system and this should be configured from the Splunk end.
+
 * Currently, there is a flaw in handling multiplexed streams in the HTTP/2 protocol, where you can repeatedly make a request for a new multiplex stream and immediately send an `RST_STREAM` frame to cancel it. This created extra work for the server set up and tore down the streams, resulting in a denial of service due to server resource consumption. There is currently no workaround for this issue. (link:https://issues.redhat.com/browse/LOG-4609[LOG-4609])
 
 * Currently, when using  FluentD as the collector, the collector pod cannot start on the {product-title} IPv6-enabled cluster. The pod logs produce the `fluentd pod [error]: unexpected error error_class=SocketError error="getaddrinfo: Name or service not known` error. There is currently no workaround for this issue. (link:https://issues.redhat.com/browse/LOG-4706[LOG-4706])