Use viper for some of the flags which can also be read from a config.yaml

[rockspore]

There exists some custom solution for the value given in the flag to override that supplied by a config file. For example, --organization/-o will override the org_name in the config.

Now we want to add environment variable support via viper. So we need to make sure the flag values are still working correctly by having them also fetched via viper.

See for reference: apigee/apigee-remote-service-envoy#165