Add comments to clarify the updated logic in kubelet's status_manager

[mimowo]

What type of PR is this?

/kind cleanup
/kind documentation

What this PR does / why we need it:

This is a follow up PR with comments to clarify the logic modified in the PR: #112360.

Which issue(s) this PR fixes:

• Tracking issue: Retriable and non-retriable Pod failures for Jobs enhancements#3329

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

- [KEP]: https://github.com/kubernetes/enhancements/tree/master/keps/sig-apps/3329-retriable-and-non-retriable-failures 

[k8s-ci-robot]

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[mimowo]

/assign @bobbypage @dchen1107

[alculquicondor]

/lgtm

[dchen1107]

/lgtm
/approve

Thanks for the followup.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dchen1107, mimowo

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