Explore other 3rd-party config sources that we could provide support for

[joelgallant]

HashiCorp Vault is the easy example.

These would be separate parsing extensions in separate npm modules, though they could live in this monorepo. I'd like to define other providers here, see which makes most sense for first-class support.

[joelgallant]

#78 adds vault support. #20 and #64 should enable going further here (dynamic extension loading is basically a blocker for ergonomics here).

[joelgallant]

https://aws.amazon.com/blogs/aws/safe-deployment-of-application-configuration-settings-with-aws-appconfig/