Support --add-host flag for finch build command

[coderbirju]

What is the problem you're trying to solve?. A clear and concise description of the use case for this feature. Please provide an example, if possible.

Currently finch run command supports --add-host flag that allows a user to add a custom host-to-IP mapping. This is currently not available in the build sub command.

Describe the feature you'd like A clear and concise description of what you'd like to happen. The --add-host flag should be supported for the finch build command, similar to docker buildx build

Additional context Add any other context or screenshots about the feature request here.

This is currently not supported in nerdctl, so we may need to contribute upstream first.