[Flux2] Allow non default service account for controllers

[alessiopavan]

Is your feature request related to a problem ?

When flux2 is deployed using helm chart, there is no possibility to specify a custom ServiceAccount to associate to controller pods, but instead default ones are used (kustomize-controller, notification-controller, source-controller, ecc...)

Describe the solution you'd like.

It could be useful to specify a custom serviceAccount name (previous create in k8s cluster) to associate to every controller pod, to handler various cloud provider integration (ex. IRSA for AWS EKS clusters).

Describe alternatives you've considered.

For example adding a if else condition in controller template (here for kustomize controller):

{{- if .Values.serviceAccountName }}
serviceAccountName: {{- .Values.serviceAccountName }}
{{- end }}

Additional context.

No response