Fix ImagePullTimeout to use "Initialized"

[skaegi]

Fixes #7881.

ImagePullBackOffTimeOut currently uses the "Scheduled" pod condition transition time, however a pod can be scheduled on a node far earlier than when image pulling begins which can (and does) result in Tasks failing when image pulls could be retried and succeed.

We should use the transition time for "PodReadyToStartContainers" (1.29+) / "Initialized" for checking the image pull timeout as these conditions more accurately capture when the image pull began.

Changes

This commit updates the imagePullBackOffTimeOut logic to use the "PodInitialized" or "PodReadyToStartContainers" Pod Condition in favour of "PodScheduled" and adds the covering tests.

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Release Notes

Fix ImagePullTimeout to use "PodInitialized" or "PodReadyToStartContainers" PodCondition transition time

[skaegi]

/kind bug

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/taskrun/taskrun.go	87.2%	87.3%	0.0

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage-df to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/taskrun/taskrun.go	87.2%	87.3%	0.0

[chitrangpatel]

/approve

[tekton-robot]

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[pritidesai]

/lgtm

thank you @skaegi 👍