NOMAD-236 userns podman configuration option

[acornies]

I haven't been able to run the tests locally, but I want to get a general sense on if this is the right approach or not.

• add userns to task config
• add parsing for userns config option
• add the driver configuration, uncomment api portion
• tests

[acornies]

Thanks @lgfa29 you beat me to it (skipping the tests). I don't think there's anything else atm. It's an effort to iterate on additional config options that would be useful to podman users. The referenced internal issue has some other stuff that might be useful but those can happen in another PR.

[lgfa29]

Cool, thanks! Feel free to open more PRs in the future as needed 😄