Add support for runArgs devcontainer property

[https://github.com/coder/envbuilder/blob/main/docs/devcontainer-spec-support.md]() does not currently mention the [`runArgs`]() part of the dev container specification:

> An array of [Docker CLI arguments]() that should be used when running the container. Defaults to \[\]. For example, this allows ptrace based debuggers like C++ to work in the container:
"runArgs": \[ "--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined" \] .

Supporting this would make the envbuilder here much more flexible for various use cases where customization of the docker containers is needed.