Add new imagePullPolicy mode IfNewerNotPresent, that pulls image if image ID (ref/digest) on remote is not matching.

[nikos445]

What would you like to be added?

An extra new mode for imagePullPolicy named IfNewerNotPresent that pulls image if image ID (ref/digest) on remote is not matching.

Why is this needed?

This gives a solution to issues such as:

• Pods that are running with an image for example v1.0.0 and a backport fix - update is released, on that image v1.0.0, without changing the tag.
  Currently, the pod will continue run with the non-backported image (that may be faulty) even if imagePullPolicy is set to IfNotPresent. IfNotPresent doesnt check the integrity of the image if pod is restarted and keeps using the older (non-backported) image.
  With this feature you can have a combination of the functionality of IfNotPresent and Integrity check that pulls image if changed in the remote registry.

A prototype - working code:
#133677

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[nikos445]

/sig scheduling

[nikos445]

/sig apps

[nikos445]

/sig cli