Support EnvironWithContext on MacOS (bsd)

[codefromthecrypt]

Is your feature request related to a problem? Please describe. I want to get the environment of a process, but I can't if I am running on MacOS

Describe the solution you'd like I would like Environ() to work

Describe alternatives you've considered defer to shell scripting

Additional context Root cause is a stubbed out process_bsd.go which returns common.ErrNotImplementedError for most things. I'm most interested in environ