docs/configuration: fix security groups example

it now uses a filter to get the security group by name

Signed-off-by: Mathieu Tortuyaux <[email protected]>

Author: tormath1

docs/book/src/clusteropenstack/configuration.md

@@ -598,7 +598,8 @@ spec:
   template:
     spec:
       securityGroups:
-      - name: allow-ssh
+      - filter:
+          name: allow-ssh
 ```
 
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