Always add image flag to jib builders in skaffold init

[TadCordle]

Fixes #2852

skaffold init used to use Jib's configured to.image to auto-pair Jib projects with k8s images. However, the skaffold.yaml that was generated prioritized the to.image configuration over the k8s images, possibly resulting in a skaffold.yaml that points a Jib builder to an image that isn't defined in a k8s manifest. This PR fixes that by only using k8s images in the generated artifacts, and also always explicitly passing a -Dimage= flag to Jib to make sure it builds the correct image, despite its configuration.

@GoogleContainerTools/java-tools-build

[chanseokoh]

I wondered if this should prompt the user for checking the mismatch, but thinking about it, this sounds reasonable. It will continue to prompt for non-single builder or project setups if image names don't match, right?

[codecov]

Codecov Report

Merging #2854 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

Impacted Files	Coverage Δ
pkg/skaffold/jib/jib_init.go	88.88% <100%> (-0.67%)	⬇️

[TadCordle]

@chanseokoh Yes, for the most part. If a match can be determined, it will still be automatic (i.e. Jib's to.image matches an image in a k8s yaml), but if there are multiple builders that can't be determined automatically then it will resort to a prompt. The only automatic pairing that happens with a mismatched image is if exactly one builder and one k8s image are found.

[chanseokoh]

Yeah, SGTM.