Add support for runArgs devcontainer property

[kujenga]

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.

[mafredri]

Hey @kujenga. This is an interesting proposal. Could you give an example of a concrete use-case you would want to see supported via runArgs?

[kujenga]

Sure! @mafredri The specific use case I ran into was to add a --shm-size flag to increase the size of /dev/shm for running a program that used lots of semaphores and exhausted the default limits. We were able to work around it but this would be nice to have to support a variety of use cases.