feat(source/node): Make exclusion of unschedulable Nodes configurable

[Hayajiro]

Description

This fixes a behavioral regression introduced in #4761, where nodes that were previously added to DNS are removed when they are considered unschedulable, for example due to automated maintenance tasks.

This change will introduce a new flag called exclude-unschedulable, which defaults to true in order to keep in line with the current behavior. However, it would also be reasonable to restore the initial behavior before #4761, which would mean to not exclude unschedulable nodes by default.

Fixes #4991

Checklist

• Unit tests updated
• End user documentation updated

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[k8s-ci-robot]

Hi @Hayajiro. Thanks for your PR.

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PR needs rebase.

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[mloiseleur]

@Hayajiro you need to sign the CLA in order for this PR to be reviewed.

[Hayajiro]

@Hayajiro you need to sign the CLA in order for this PR to be reviewed.

I'm fully aware of this, but CLA signing is still in process.