Warn user for runtime support of debug targeting

[verb]

Add a warning message to kubectl debug when using the --target option as many runtimes don't support it yet.

What type of PR is this?

/kind documentation
/sig cli
/priority important-soon

What this PR does / why we need it:

Many container runtimes (e.g. containerd) don't implement support for process namespace target required for kubectl debug --target to work. This adds a warning message which we can remove after the major runtimes add support and we (potentially) add the feature to runtime qualification.

Which issue(s) this PR fixes:

Fixes #98362

Special notes for your reviewer:

Does this PR introduce a user-facing change?

`kubectl debug` will now print a warning message when using the `--target` option since many container runtimes do not support this yet.

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

[k8s-ci-robot]

@verb: This issue is currently awaiting triage.

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[verb]

/retest

[rikatz]

/lgtm

Thank you!

[verb]

@soltysh What do you think about adding this warning message to kubectl debug?

/assign @soltysh

[eddiezane]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: eddiezane, rikatz, verb

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• staging/src/k8s.io/kubectl/OWNERS [eddiezane]

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[fejta-bot]

/retest
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