[7.3] Update where log files are written using systemd (#47570) (#51466)

At least for kibana-oss 7.4, this is how I can access Kibana logs. 
The file `/var/log/kibana` is not created and if I set it as a log file, kibana does not have permission to write there. 
See also:
#6579

docs/setup/install/systemd.asciidoc

@@ -18,5 +18,5 @@ sudo systemctl stop kibana.service
 --------------------------------------------
 
 These commands provide no feedback as to whether Kibana was started
-successfully or not. Instead, this information will be written in the log
-files located in `/var/log/kibana/`.
+successfully or not. Log information can be accessed via
+`journalctl -u kibana.service`.