[DOCS] Clarify space awareness of maintenance windows (elastic#176628)

(cherry picked from commit e6a6a47)

docs/management/maintenance-windows/maintenance-windows.asciidoc

@@ -11,7 +11,7 @@ preview::[]
 You can schedule single or recurring maintenance windows to temporarily reduce rule notifications.
 For example, a maintenance window prevents false alarms during planned outages.
 
-Maintenance windows affect all rules in all {kib} apps and spaces.
+By default, a maintenance window affects all rules in all {kib} apps within its space.
 Alerts continue to be generated, however notifications are suppressed as follows:
 
 - When an alert occurs during a maintenance window, there are no notifications.