[Migrated] Allow environment variable expansion in settings

[jneves]

Originally from: Miserlou/Zappa#1982 by gdavoian

I'd like to use aws_environment_variables to set some native Lambda environment variables automatically without logging into the AWS console, but I don't want to hard-code any sensitive values to the zappa_settings.json. Ideally, I'd like to use something like "key": "${value}", and then have Zappa substitute value from the current environment on deploy/update. I'm not sure whether this is already supported or whether it really makes sense to add support for this.

[monkut]

marking as duplicate of:
#988