Custom image repository/tag configuration inconsistent

[sebhoss]

Describe the bug:

We have the following SyslogNGConfig resource in our cluster to overwrite the various image repositories to use our internal registry mirror:

apiVersion: logging.banzaicloud.io/v1beta1
kind: SyslogNGConfig
metadata:
  name: default
  namespace: logging
spec:
  configReloadImage:
    repository: registry.internal/ghcr/kube-logging/logging-operator/syslog-ng-reloader
  syslogNGImage:
    repository: registry.internal/ghcr/axoflow/axosyslog
  bufferVolumeMetricsImage:
    repository: registry.internal/ghcr/kube-logging/logging-operator/node-exporter
  metricsExporterImage:
    repository: registry.internal/ghcr/axoflow/axosyslog-metrics-exporter

We noticed that for the configReloadImage image, logging-operator will correctly replace the image repository and use its own default value for the image tag. However, the same is not true for the syslogNGImage. For this image, defining a custom repository overwrites both the repository and tag. Using our configuration above results in an empty tag (which then defaults to latest). We would prefer that the operator uses its own default value for the image tag here as well.

Expected behaviour:

Overwriting image repositories should not change image tags.

Steps to reproduce the bug:

1. Deploy the above resource
2. Look at generated manifests
3. See that the syslog-ng image has no tag

Additional context:
Add any other context about the problem here.

Environment details:

• Kubernetes version (e.g. v1.15.2): 1.35.2
• Cloud-provider/provisioner (e.g. AKS, GKE, EKS, PKE etc): bare-metal
• logging-operator version (e.g. 2.1.1): 6.4.0
• Install method (e.g. helm or static manifests): helm
• Logs from the misbehaving component (and any other relevant logs): N/A
• Resource definition (possibly in YAML format) that caused the issue, without sensitive data: see above

/kind bug