Fix and improve manage-offline-container-images script

[anders-elastisys]

What type of PR is this?

/kind bug

What this PR does / why we need it:

This PR adds some improvements to the contrib/offline/manage-offline-container-images.sh script. Improvements include:

• New environment variable DESTINATION_REGISTRY for pushing to a registry of your choice instead of the default one created by the script
• New environment variable IMAGES_FROM_FILE that can be used to read a list of images from a file (e.g. temp/images.list created by the generate_list.sh script) instead of getting images from a cluster
• New environment variable REGISTRY_PORT to override the local container registry to run on a different port than 5000
• Getting images from cluster now looks at jobs and cronjobs as these may not always be running as a pod (e.g. created by operators)
• Added bug fixes such as additional parsing and checks for when working with images that contains the image digest in the tag, as this did not work previously and stopped the script from finishing

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

The script `manage-offline-container-images.sh` now supports additional environment variables, e.g. it is now possible use the script to pull images listed in a file instead of checking images in a running cluster.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: anders-elastisys (a9deb22)

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[k8s-ci-robot]

Hi @anders-elastisys. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[yankay]

/ok-to-test

[VannTen]

Minor nitpicking

[VannTen]

/lgtm
(Not that I don't use that script, but I don't spot anything wrong. Not sure if we have that tested in CI ? 🤔 )

[anders-elastisys]

@VannTen I could not find any tests for this script, so not sure. I squashed the commits into one, hence the bot detected new changes.

[VannTen]

Can you add general description of the new variables and why they are needed directly in the commit message please ?

[anders-elastisys]

@VannTen PTAL

[VannTen]

/lgtm

[VannTen]

/assign @mirwan @yankay
(approval)

[k8s-ci-robot]

@VannTen: GitHub didn't allow me to assign the following users: mirwan.

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In response to this:

/assign @mirwan @yankay
(approval)

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[yankay]

Thanks @anders-elastisys
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: anders-elastisys, yankay

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