bug: path is filled with default value for buffer of type memory, it generates warn logs

[antrema]

Describe the issue

When creating a memory-type buffer section in Fluentd ClusterOutput, with empty field Path (not necessary), this field is filled with default value.
Even if it has no effect on Fluentd, its specification creates a warm log entry in fluentd pod, each time it reconcile:

2024-04-03 02:19:01 +0000 [warn]: parameter 'path' in <buffer $.loki-tenant>
  @type "memory"
  flush_interval 5s
  path /buffers/fluentd/log
</buffer> is not used.

To Reproduce

Create a ClusterOutput, as follow:

---
apiVersion: fluentd.fluent.io/v1alpha1
kind: ClusterOutput
metadata:
  name: fluentd-output-loki
  labels:
    output.fluentd.fluent.io/enabled: "true"
spec:
  outputs:
    - loki:
        url: http://loki-write.loki.svc:3100
        tenantID:
          valueFrom:
            secretKeyRef:
              key: tenant_key
              name: tenant-name
        labels:
        - cluster=linux-lab
      buffer:
        type: memory
        tag: $.loki-tenant
        flushInterval: 5s

Have a look at fluentd logs and Fluentd configuration file (the field Path is filled with default value)

Expected behavior

No default value in Fluentd config file
No warm log in fluentd pod

Your Environment

- Fluent Operator version: kubesphere/fluent-operator:v2.7.0
- Container Runtime: containerd://1.6.15
- Operating system: Ubuntu 22.04.1 LTS
- Kernel version: 5.15.0-46-generic

How did you install fluent operator?

kubectl create ns fluent 
kubectl apply -f https://raw.githubusercontent.com/fluent/fluent-operator/release-2.7/manifests/setup/setup.yaml

Additional context

No response

[antrema]

I will propose a PR to correct this behaviour