feat: add label(s) modified message for kubectl label command

[TessaIO]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR aims to modify the kubectl label command when we add and remove labels at the same time. In fact, the old behavior was based on the length of labels being added/removed. Now, if we remove and add labels at the same operation we just output label(s) modified

Which issue(s) this PR fixes:

Fixes #1312

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Added the "label(s) modified" message to handle the case of adding and removing labels at the same time.

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

N/A

[k8s-ci-robot]

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[TessaIO]

/cc @brianpursley

[ah8ad3]

Thanks for the PR. I think it would be nice if we change from

	MsgNotLabeled    = "not labeled"
	MsgLabeled       = "labeled"
	MsgUnLabeled     = "unlabeled"
	MsgLabelsChanged = "label(s) changed"

to just simply

	MsgNotLabeled    = "not labeled"
	MsgLabelsChanged = "label(s) changed"

but wait for other reviewer for this.

[TessaIO]

Thanks for the PR. I think it would be nice if we change from

	MsgNotLabeled    = "not labeled"
	MsgLabeled       = "labeled"
	MsgUnLabeled     = "unlabeled"
	MsgLabelsChanged = "label(s) changed"

Thanks for the review, and I see your point. However, it would be cleaner from a UX perspective if the user knew what happened exactly. The current setup in the PR allows the user to differentiate between adding labels, removing labels, and adding and removing labels by the same operation. Therefore, I see that printing label(s) changed for all of these kinds of operations makes it blurry/hard for the user to understand what happened exactly.

[k8s-ci-robot]

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