Allow setting extra fields from values

[mosheavni]

Hi,
can you please adjust the templates to allow filebeat.yml to have additional fields as part of the regular helm values?
https://www.elastic.co/guide/en/beats/filebeat/current/add-fields.html

I'd like to set it like this:

helm install --namespace=kube-system \
--set secrets.logzioShippingToken='lzrBhFcnLQCGtdFPhpgRbnaLDKvnZhzw' \
--set secrets.logzioRegion='<<LISTENER-REGION>>' \
--set secrets.clusterName='<<CLUSTER-NAME>>' \
--set extraFields.environment='staging' \
--set extraFields.foo='bar' \
logzio-k8s-logs logzio-helm/logzio-k8s-logs

and it will generate the config like this:

      filebeat.autodiscover:
        providers:
          - type: kubernetes
            node: ${NODE_NAME}
            hints.enabled: true
            hints.default_config:
              type: container
              paths:
                - /var/log/containers/*-${data.kubernetes.container.id}.log
            include_annotations: '*'
      processors:
        - add_cloud_metadata: ~
        - add_fields:
            target: ''
            fields:
              foo: bar
              environment: staging
      fields:
        logzio_codec: ${LOGZIO_CODEC}
        token: ${LOGZIO_LOGS_SHIPPING_TOKEN}
        cluster: ${CLUSTER_NAME}
        type: ${LOGZIO_TYPE}
      fields_under_root: ${FIELDS_UNDER_ROOT}
      ignore_older: ${IGNORE_OLDER}
      output:
        logstash:
          hosts: ["${LOGZIO_LOGS_LISTENER_HOST}:5015"]
          ssl:

Thanks.