InfluxDB helm chart - Support initContainers

[QuinnBast]

The current InfluxDB Helm chart provides no way to add additional initContainers and currently the only way to do this is to use Kustomize. In addition to the extraContainers field, you should add an initContainers field that is the exact same but allows getting placed under the initContainers: field.

This is useful for people like me who want to migrate Influx from a docker deployment into kubernetes and initialize the PV's volume before influx starts up by using an init container.