[fluentd] Add support for dnsConfig and dnsPolicy

[vladiceanu]

hey folks,
I'd like to be able to set a custom dnsConfig and dnsPolicy [1] for fluentd pods using this Helm chart. The main reason is to be able to set a different value for the ndots, but of course, other options should be configurable as per user needs.

I could contribute with a PR in this sense if no objections.

[1] - https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#pod-dns-config