Use BuildAh --digestfile argument to store digest of pushed image

[SaschaSchwarze0]

Changes

Fixes #1028

Using the proposed approach by @nalind to store the digest of the pushed image in the BuildRun result. Much simpler than the previous workaround. :-)

Submitter Checklist

• Includes tests if functionality changed/was added
• Includes docs if changes are user-facing
• Set a kind label on this PR
• Release notes block has been filled in, or marked NONE

Release Notes

Use BuildAh's `--digestfile` argument in the sample build strategies

[qu1queee]

nice,

@gabemontero pls approve from your side if this looks accurate.

/lgtm

[gabemontero]

yep this looks in line with my interpretation of @nalind 's super helpful summary in #1028 (comment)

I will

/approve

for merge.

@nalind - if you have 2 seconds to eyeball the change, please do and post any comments here. If by chance there is some tweak we need, we can follow up separately. Thanks again.

[openshift-ci]

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