feat: differentiate between Runner and Initializer initContainers

[FloGro3]

Fixes 296

Enables you to have separate initContainers for the initializer and runner pod.

Was tested successfully in own K8 environment (only the initializer pod was configured to have initContainers):

Config looks like this:

initializer:
    ...
    {{- if .Values.executor.script.volumeClaim }}
    initContainers:
      - image: {{ tpl $.Values.docker.registry $ }}/{{ tpl $.Values.image.name $ }}:{{ tpl $.Values.image.tag $ }}
        {{- if .Values.image.command }}
        command: [ "sh", "-c", {{ .Values.image.command }} ]
        {{- else }}
          {{- with (index .Values.mount.pvcs 0) }}
        command: [ "sh", "-c", "cp -r /home/* {{ .path }};" ]
          {{- end }}
        {{- end }}
    {{- end }}

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[FloGro3]

@yorugac Sure, I've added a small example.