improves hook build

[jaxesn]

Issue #, if available:

Description of changes:

This improves the building of hook locally. Hook requires a number of images from other projects. Currently this requires building them all locally and pushing to your regi. Also because the linuxkit part is run within a docker container pulling from local/private regi was not possible.

This introduces a new env var to set the image repo for these images so you can pull these from the eksa build account, assuming you have ecr creds. Images are also pulled on the host before calling linuxkit in the container to allow for "any" regi to work since we do not have to worry about auth.

Updates the helper that creates the buildkitd container to use buildx, since we have been using that for a while by default, and also sets network=host to allow for that container to push to a locally running regi.

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[jaxesn]

/hold