Design async data injection mechanism

[justsml]

Sometimes business rules need access to external data (from a Database, HTTP API, AI/ML Service, etc.)

Goals

• [ ] Support JSON config-style declaration.
• [ ] Securely reference API keys.
• [ ] Pluggable / layered design. (Similar to inputMap & outputMap designs.)
• [ ] Rely on existing 'client' APIs. (fetch, pg, etc)