Add volumeMounts to job pods

[razvan]

Description

Fixes #342

Tested with: https://github.com/stackabletech/hdfs-topology-provider/blob/feat/job-volume-mounts/test/stack/07-spark.yaml

Definition of Done Checklist

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1. Changes are OpenShift compatible
2. CRD changes approved
3. CRD documentation for all fields, following the style guide.
4. Helm chart can be installed and deployed operator works
5. Integration tests passed (for non trivial changes)
6. Changes need to be "offline" compatible

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1. Code contains useful comments
2. Documentation added or updated. Follows the style guide.
3. Changelog updated
4. Cargo.toml only contains references to git tags (not specific commits or branches)

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1. Feature Tracker has been updated
2. Proper release label has been added

[razvan]

CI: https://ci.stackable.tech/view/02%20Operator%20Tests%20(custom)/job/spark-k8s-operator-it-custom/127/

[adwk67]

LGTM - nice!

[adwk67]

ah, we probably need an update to the "CRD specification" in the docs section.

[adwk67]

Need to add this option to the docs/CRD section.

[razvan]

Need to add this option to the docs/CRD section.

Tthe crd docs are now generated automatically. That's why I added this which is copied to the CRD.

[adwk67]

I mean this, which is independent of the auto-generated docs: https://docs.stackable.tech/home/stable/spark-k8s/crd-reference