replacements: fix issue with create: true option when there is an existing field

[natasha41575]

First commit demonstrates the bug, second one fixes it. Likely caused by #4424. Follow up to this review comment #4577 (comment).
LookupCreate seems to do weird things if the field already exists. So the logic here is just: if the field already exists, don't use LookupCreate.

/cc @KnVerey @yuwenma

[k8s-ci-robot]

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[k8s-ci-robot]

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[natasha41575]

/label tide/merge-method-squash

[yuwenma]

PR looks good and the logic is straight forward to me. Defer to @KnVerey to approve.

[koba1t]

Hi
I opened #4608 to fix #4577 (review)
I think the above PR is related to this.

Could you check it?
And, Can I help you?

[KnVerey]

/lgtm