accept arbitrary docker run arguments

[moomerman]

I've got a couple of scenarios where I want to provide additional arguments to the docker run command, but at present it doesn't look like there's a way to provide them via configuration.

One example is where I want to provide additional capabilities to the container:

 --cap-add=NET_ADMIN --cap-add=SYS_ADMIN --device=/dev/net/tun

Rather than supporting capabilities and devices as special cases, perhaps we can just provide a run_args config where you can specify additional arguments?

Happy to implement it if desired.

[dhh]

Happy to see this. We already have a specialized version of this for Traefik. So you can follow that pattern 👍

[dhh]

Sorted via #95