Cache SSM parameter values into environment variables

Cache SSM parameter values into environment variables

The goal here is to reduce SSM parameter reads/writes. Hopefully, as
AWS reuses a container for multiple calls to our Lambda function,
these values can be read from the environment instead of needing to
reach out to AWS.

The reason we want to reduce calls to SSM functions in that AWS Free
Tier gives us only 20,000 KMS requests compared to 1,000,000 AWS
Lambda requests.