Custom dockerhub registry

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Have the registry, (and user/password if needed) configurable in the user config so that Exegol users can work with custom, pre-built, images.

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Picking up from a Discord discussion from @Dramelac

adding support for external docker registry was not in replacement of the original one, the idea was to be able to configure multiple registry and exegol would be able to handle all of them at the same time
this approch allow user to have custom image and at the same time can use official images without editing the configuration everytime

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v1, have a "dev" mode in the wrapper (i.e. manage multiple official public registries so that we can keep the main official images in the main registry, plus additional images in a secondary one). Handling external registries (w/wo authentication) is another topic.
People that would want access to the additional official images can have that access by adding a flag in the wrapper config.