Copy extraContainers from fluent-bit to fluentd chart

[tghartland]

Copy both the templating for extraContainers and the examples in the values file from the fluent-bit chart.

This allows the fluentd chart to define sidecar containers as well.

Example use case:

volumes:
  - name: tls
    secret:
      secretName: fluentd-tls

volumeMounts:
  - name: tls
    mountPath: "/fluentd/certs"

extraContainers:
  - name: cert-reloader
    image: alpine:3.20
    command: ["/bin/sh"]
    args:
    - -c
    - |
      apk add --no-cache curl inotify-tools
      while true; do
        inotifywait -e delete_self /fluentd/certs/tls.crt
        echo "certificate changed at $(date)"
        curl -s -w "\n" http://127.0.0.1:24444/api/config.gracefulReload
        echo "certificates reloaded"
        sleep 1
      done
    volumeMounts:
    - name: tls
      mountPath: /fluentd/certs/

to trigger a reload of TLS certificates from a sidecar container, for use with the forward input plugin.