add image garbage collection

[zhan9san]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Customize the imageGCHighThresholdPercent and imageGCLowThresholdPercent values in the kubelet config
Which issue(s) this PR fixes:

Fixes #9815

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Allow to configure image garbage collection (using `kubelet_image_gc_high_threshold` and `kubelet_image_gc_low_threshold`)

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[oomichi]

Looks interesting feature, just one comment.

/cc @oomichi

[oomichi]

Could we describe different explanation with the above kubelet_image_gc_high_threshold?
Current description is completely same and it is hard to know the difference from that.
In addition, it is nice to describe some example values for those options.
(I was wondering we need to specify 90 or 90%)

[zhan9san]

Sorry, it's a typo.

It is fixed, and the commits are squashed.

[yankay]

Thanks @zhan9san
/ok-to-test
/lgtm

[floryut]

@zhan9san Thank you for the PR

Not sure if a default var should be set in default, but this is not always done so fine by me

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: floryut, zhan9san

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[zhan9san]

@floryut

Not sure if a default var should be set in default, but this is not always done so fine by me

IMO, there is no need to set the default value in kubespray, as it will respect the default value in kubelet.

As we can see, this item is not used frequently, the advanced usage can set it explicitly.

The default value is set in kubelet, https://github.com/kubernetes/kubelet/blob/fafeddfbd4f5bc495a54bd856f815fd018ea1e61/config/v1beta1/types.go#L291-L306

If they are not defined, no item would be set in config by kubespray, https://github.com/kubernetes-sigs/kubespray/pull/9832/files#diff-b0825d62030b3a7901d61f15022353f8f2592796f007db00a4fafbe6d17c3a94R150-R155

[sathieu]

Maybe this PR was not needed, because kubelet_config_extra_args exists.

[floryut]

Maybe this PR was not needed, because kubelet_config_extra_args exists.

You are kind of right, but it is easier for end user to configure them when presented that way, I'm incline to only have corner case args set using extra_args, and common one using vars