CLI Environment Variables

[SellersEvan]

Is your feature request related to a problem? Please describe.
Currently, there is no way to add environment variables to the builder from the CLI.

Describe the solution you'd like
Add an argument to the build CLI which allows users to provide additional environment arguments. I envision something like this...

sherpa build -b local -v foo=2 nice=3

Describe alternatives you've considered
N/A

Additional context
N/A