Adds extra_conda and extra_pip to get_environment

[btovar]

If given, these arguments are a list of packages to add to the environment. E.g.

remote_environment.get_environment(
    extra_conda=["matplotlib=3"], extra_pip=["pytest==7.4.5"]
)

[kmohrman]

Thanks very much @btovar, I just tried this out and it works great. I'd be happy to merge assuming (@bryates is good with it as well).