Refactor API and lambdas to use lambda -> API pattern

[jbkolze]

Lambda will perform database updates through API endpoints rather than through a direct RDS connection.

Need to:

• set up lambda auth workflow in API (check for internal token in request header)
• ingest env vars in lambdas as needed -- ALB URL, SQS URL, etc.
• make request to appropriate API endpoint from lambda
• ingest app key secret in lambda
• include an app key in lambda request header to allow verification within API