CA-414586 add message-limit to xapi.conf (#6876)

For better discoverarbility, add a line to xapi.conf for the
message-limit parameter.

Author: lindig

scripts/xapi.conf

@@ -389,6 +389,9 @@ sm-plugins=ext nfs iscsi lvmoiscsi dummy file hba rawhba udev iso lvm lvmohba lv
 # How often tracing will export spans to endpoints
 # export-interval = 30.
 
+# maximium number of messages kept before oldest are removed
+# message-limit = 10000
+
 # The file to check if host reboot required
 reboot_required_hfxs = /run/reboot-required.hfxs