KEP-2000: Add note in KEP Proposal for shutdown -h now systemd version compatibility

[tuibeovince]

• One-line PR description:
  Add note indicating that 'shutdown -h now` may not trigger GracefulNodeShutdown in the KEP-2000.

• Issue link:
  GracefulNodeShutdown does not trigger on nodes shutdown with shutdown -h now kubernetes#124039

• Other comments:
  Having shutdown -h now listed as the first way of shutting down gives the false impression that this method is recommended. But in some environments, the GracefulNodeShutdown may not trigger with shutdown -h now

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[k8s-ci-robot]

Hi @tuibeovince. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[tuibeovince]

cc to the KEP-2000 author @bobbypage

[bart0sh]

/ok-to-test
/triage accepted
/priority backlog

[mrunalp]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mrunalp, tuibeovince

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