Need the ability to set arbitrary environment variables for configuration (related to Proxy Support)

[jmontleon]

We need the ability to set arbitrary environment variables.

This requirement is based in part for our need to support proxies along with related functionality.

I have started a PR to capture some of the most common settings likely to be used when Kai connects to an API server via a proxy.
#538

However, there are other environment variables we are coming across as we test that are necessary to set aside from those directly related to proxy support.