az configure | spelling error in parameter name is not throwing an error

**Issue #1:** It looks like a customer can enter any value as a default. "subscription" isn't even a supported config value according to https://docs.microsoft.com/en-us/cli/azure/azure-cli-configuration?view=azure-cli-latest#cli-configuration-with-az-configure.


**Issue #2:** We allow for resource group defaults using az config set, az configure --defaults, and az config param-persist. This actually then changes the default subscription. Yet, if a customer does a "list" or "show", they only see the resource group value. This is very confusing when they have set their subscription value, then over-write themselves with a resource group default.