Allow Local Builds of Images from Containerfile

**Is your feature request related to a problem? Please describe.**
I don't necessarily want to have to push my development images to a remote registry.

**Describe the solution you'd like**
It would be more convenient to simply provide a `Containerfile` in a repository alongside the source code that contributors could use to build a local image. `toolbox create` could then offer functionality to use this `Containerfile` instead of needing an image name.

**Describe alternatives you've considered**
One can just run `podman create` prior to running `toolbox create`, though it would be nice to have `toolbox` handle that automatically.

**Additional context**
VS Code has [development containers](https://containers.dev/) that allow for maintainers to ship `Dockerfile`s alongside their code, so that contributors don't need to spend time configuring their machines with the necessary dependencies in order to be able to contribute code. Dev containers configure much more than the container images though, such as VS Code extensions and forwarded ports, and they aren't as tightly integrated with the desktop environment, so they aren't a great substitute.

Start by reviewing the `toolbox create` command and its existing handling of image names, then compare the manual `podman create` workflow described in the issue. Determine how a repository `Containerfile` would be selected and built locally, and define completion as `toolbox create` supporting that workflow without requiring a remote image.

Written by the indexing model from the issue text.