feat: `NO_PROXY` environment variable can be used to override `HTTP(S)_PROXY` values

[keelerm84]

When determining if a proxy should be used, the SDK would:

1. Check the config.http_config.http_proxy value. If that is set, use that value without further consideration.
2. If the target URI is https, use the value from the HTTPS_PROXY environment variable.
3. If the target is http, use HTTP_PROXY instead.

The SDK will now support another environment variable -- NO_PROXY. This variable can be set to a comma-separated list of hosts to exclude from proxy support, or the special case '*' meaning to ignore all hosts.

The NO_PROXY variable will only take affect if the SDK isn't explicitly configured to use a proxy as specified in #1 above.