feat(release): update image promotion to use kpromo

[richardcase]

What type of PR is this?

/kind feature

What this PR does / why we need it:

The release process has been updated to use kpromo for handling the image promotion instead of the manual process we had.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

Checklist:

• squashed commits
• includes documentation

Release note:

Change the release process to use **kpromo**

[richardcase]

/cherrypick release-1.5

[k8s-infra-cherrypick-robot]

@richardcase: once the present PR merges, I will cherry-pick it on top of release-1.5 in a new PR and assign it to you.

In response to this:

/cherrypick release-1.5

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[Ankitasw]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Ankitasw

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• OWNERS [Ankitasw]

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[k8s-infra-cherrypick-robot]

@richardcase: #4158 failed to apply on top of branch "release-1.5":

Applying: feat(release): update image promotion to use kpromo
Using index info to reconstruct a base tree...
M	Makefile
M	docs/book/src/development/releasing.md
M	hack/tools/Makefile
M	versions.mk
Falling back to patching base and 3-way merge...
Auto-merging versions.mk
CONFLICT (content): Merge conflict in versions.mk
Auto-merging hack/tools/Makefile
Auto-merging docs/book/src/development/releasing.md
CONFLICT (content): Merge conflict in docs/book/src/development/releasing.md
Removing docs/book/src/development/imagepromo1.png
Auto-merging Makefile
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 feat(release): update image promotion to use kpromo
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherrypick release-1.5

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[Ankitasw]

@richardcase uhmmm merge conflict 🤦‍♀️

[richardcase]

@richardcase uhmmm merge conflict woman_facepalming

I'll do it manually.