[ksmcore] Remap unknown to warning for 'node.ready' service check

[kaitlavs]

What does this PR do?

Remaps the value of the KSMCore node.ready service check from 'unknown' to 'warning' when a node enters an unknown state.

Motivation

Additional Notes

Related to the legacy check PR: DataDog/integrations-core#11132

Possible Drawbacks / Trade-offs

Describe how to test/QA your changes

It is difficult to replicate the unknown state of a node, but it can be tested on a large cluster, which is more likely to have a node in this state

Reviewer's Checklist

• If known, an appropriate milestone has been selected; otherwise the Triage milestone is set.
• The appropriate team/.. label has been applied, if known.
• Use the major_change label if your change either has a major impact on the code base, is impacting multiple teams or is changing important well-established internals of the Agent. This label will be use during QA to make sure each team pay extra attention to the changed behavior. For any customer facing change use a releasenote.
• A release note has been added or the changelog/no-changelog label has been applied.
• Changed code has automated tests for its functionality.
• Adequate QA/testing plan information is provided if the qa/skip-qa label is not applied.
• If applicable, docs team has been notified or an issue has been opened on the documentation repo.
• If applicable, the need-change/operator and need-change/helm labels have been applied.
• If applicable, the config template has been updated.

[bits-bot]

All committers have signed the CLA.

[maycmlee]

👍 for docs