Add support for initContainers

[CiucurDaniel]

It seems the user is unable to configure initContainers on the deployment. It would be great to have to option. An example use case is using Vault Init Container in order to add the values for Elasticsearch username and password.

Let me know if this can be added, I may try to submit the implementation myself.

[codefromthecrypt]

go for it. even better if there's a ci file to prove it works