add flag to pause at end of scripts before creating image

[aerickson]

When debugging, I often want to inspect the image before creating an image.

Potential implementation: Use https://developer.hashicorp.com/packer/docs/provisioners/breakpoint to implement this. Add a flag that will inject this provisioner at the end of the Packer process.

[aerickson]

Currently working around with monopacker build monopacker-testing-image --packer-args '-on-error=ask' (the packer args) and the debugging-fail script.