Incorrect example under 'Tuning log payloads and delivery', the example is missing the fact that is needs to be within an output.

Logging 5.9 (where this feature was introduced)    

apiVersion: logging.openshift.io/v1
kind: ClusterLogForwarder
metadata:
# ...
spec:
  tuning:
    delivery: AtLeastOnce 
    compression: none 
    maxWrite: <integer> 
    minRetryDuration: 1s 
    maxRetryDuration: 1s     

apiVersion: logging.openshift.io/v1
kind: ClusterLogForwarder
metadata:
# ...
spec:
  outputs:
  - name: highly-modified
    tuning:
      delivery: AtLeastOnce 
      compression: none 
      maxWrite: <integer> 
      minRetryDuration: 1s 
      maxRetryDuration: 1s     

Please reference: https://github.com/openshift/enhancements/blob/master/enhancements/cluster-logging/performance-tuning.md