fix: add --load flag for local buildkit

[Crystalix007]

Description

Adds the --load flag when building images using buildkit, and not pushing to a remote registry.

This is required, to get them loaded into the local docker context.

User facing changes (remove if N/A)

Before:

Running dev complained with:

WARNING: No output specified with docker-container driver. Build result will only remain in the build cache. To push result image into registry use --push or to load image into docker use --load
...
Build [docker.io/...] failed: could not push image "docker.io/...:4002597-dirty": An image does not exist locally with the tag: ...

After:

Tags used in deployment:
 - docker.io/... -> docker.io/crystalix007/...:e1958765598cf4713ec0f5c9d9afa702fccc6098d509d84d272a14b373f422dd

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[ericzzzzzzz]

Hi @Crystalix007 Thank you for the contribution! The change looks good, but skaffold integration test infra seems broken at the moment, we'll merge the change after the issue is fixed.