Allow images from private registries

[eduardOrthopy]

Hi there,

Before we get started, amazing tool. Love it ❤️

Now for my question, would you be open to adding support for private registries?
Specifically, I would like to conditionally add an image pull secret to the spec based on if an env-var is set or not.

I am basically imagining something similar to the way custom images are handled now.

If you are interested in that, I am willing to build this feature and contribute it to the project. Just wanted to ask before I get into coding :)