Support additional run arguments (network & pid)

[QuentinLeloire]

runArgs can't be inherited from prebuilt base image, we need to put it in the devcontainer.json even if declared in prebuilt base image.

It should be useful to implement network and pid flags like capAdd, privileged and securityOpt actually does.
This approach would enable the sharing of these flags through prebuilt base image with an implementation like this :

{
	"name": "Custom image",
	"build": {
		"dockerfile": "Dockerfile",
		"args": {
			"devcontainercli": "true"
		}
	},
	"capAdd": ["ALL"],
	"securityOpt": ["seccomp=unconfined"],
	"privileged": true,
        "network": "host",
        "pid": "host",
        [...]
}