Proposal

When using a custom implementation of an ImageSubstitutor while also having set TESTCONTAINERS_HUB_IMAGE_NAME_PREFIX, the prefix will be prepended if testcontainers decides that the image name still needs a substitution before starting the container. This is adequate behavior for all the cases where there should be a default registry to fall back to if none of the prior ImageSubstitutors set one. But it poses a problem when the image under test was built and tagged locally and has not been published to a registry yet.
It would be great if an ImageSubstitutor could have the option disable the prefixing mechanism.