Sentence-case fix (#17611)

+ Fix casing of "External activity audit logging"
+ Fix a nearby typo

docs/Configuration/fleet-server-configuration.md

@@ -1152,9 +1152,9 @@ osquery:
   status_log_plugin: firehose
   result_log_plugin: firehose
 ```
-#### External Activity Audit Logging
+#### External activity audit logging
 
-> Applies only to Fleet Premium. Acitivity information is available for all Fleet instances using the [Activities API](https://fleetdm.com/docs/using-fleet/rest-api#activities).
+> Applies only to Fleet Premium. Activity information is available for all Fleet instances using the [Activities API](https://fleetdm.com/docs/using-fleet/rest-api#activities).
 
 Stream Fleet user activities to logs using Fleet's logging plugins. The audit events are logged in an asynchronous fashion. It can take up to 5 minutes for an event to be logged.