use merge-patch on finalizer operations to resolve racing conflicts

[mars1024]

What this PR does / why we need it:
Patch is more efficient than Update to handle racing conditions on high-frequency changes of objects, which is also recommended by kubernetes spec.

Which issue(s) this PR fixes:
Try to avoid some errors, like https://github.com/kubernetes-sigs/kubefed/blob/4dbd63b07de4b2bcebf3bd2632e0ec08e254f4c3/pkg/controller/sync/controller.go#L283

[swiftslee]

There are many Update operations. Could you tell me why do you only change the finalizer update operation?

[mars1024]

There are many Update operations. Could you tell me why do you only change the finalizer update operation?

Actually, this is only the first step. I'll try to use more Patch after this merged.

[swiftslee]

There are many Update operations. Could you tell me why do you only change the finalizer update operation?

Actually, this is only the first step. I'll try to use more Patch after this merged.

@hectorj2f What's your suggestion?

[hectorj2f]

I'd like to see a more consistent and global change of Update to Patch operations across the whole code. I agree with @mars1024 here.

[mars1024]

I'd like to see a more consistent and global change of Update to Patch operations across the whole code. I agree with @mars1024 here.

Thanks for your agreement, @hectorj2f , and I think this PR is already ready as the first step.

[makkes]

/lgtm

[mars1024]

friendly ping @hectorj2f for approval or more comments

[hectorj2f]

@mars1024 What did it happen with the rest of changes to use Patch instead of Update ?

[mars1024]

@mars1024 What did it happen with the rest of changes to use Patch instead of Update ?

Recently I didn't have much time on this, so I opened an help-wanted UMBRELLA issue to track the rest changes.

[hectorj2f]

/lgtm

[hectorj2f]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hectorj2f, makkes, mars1024

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