FEATURE: build operator image as non-root

[ImpSy]

Purpose of this PR

Reduce the permission of the docker image by making it non-root (like the spark image it's build from)

Proposed changes:

• Re-enable go mod caching while building the image
• Make the image use the USER define in the base spark-image (UID: 185, NAME: spark)
• Use setcap on the binary to keep the ability to mount port <1024 (useful for people mounting webhook on 443)

Change Category

Indicate the type of change by marking the applicable boxes:

• Bugfix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that could affect existing functionality)
• Documentation update

Rationale

If we aim to increase security of the project, making the image non root is a good 1st step

Checklist

Before submitting your PR, please review the following:

• I have conducted a self-review of my own code.
• I have updated documentation accordingly.
• I have added tests that prove my changes are effective or that my feature works.
• Existing unit tests pass locally with my changes.

Additional Notes

This change has been live on our product for more than 6 month
You can find the PR from our fork here -> https://github.com/spotinst/spark-on-k8s-operator/pull/10/files

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ChenYi015

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[ChenYi015]

@ImpSy Thanks for the effort to improve the security of operator image! LGTM, will wait for another approval @vara-bonthu @jacobsalway.