feat(kustomize): support image digest pinning in newTag

[maxbrunet]

Changes

Add autoReplaceStringTemplate to images with newTag, which in my opinion, is the only case where it is clearly desired to enable digest pinning.

Context

Like #24942, without autoReplaceStringTemplate, this was blocking the renovate/pin-dependencies branch

This is not the full support as investigated in #24767.

Mainly, even while following the current limitations, it is unclear what the intent is when newName is used:

• is it set to use a different mirror and the image version is set in the manifest
• or is it meant to use an entirely different image, in which case, digest pinning may be desirable

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[renovate-release]

🎉 This PR is included in version 37.49.0 🎉

The release is available on:

• GitHub release
• 37.49.0

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