How to detect in Deno if it is currently a `prod` deployment?

### What problem are you trying to solve?

I need to configure logging for my app and I need to differentiate whether a message originated from a `prod` environment or from one of the preview environments.

### Describe the solution you'd like

Something akin to checking an ENV var that updates as the status of the Deno isolate/instance changes

### Describe alternatives you've considered

Tracing the URL of requests that generate messages as a proxy for this info

### Documentation, Adoption, Migration Strategy

_No response_

Start by reviewing how Deno Deploy distinguishes production and preview environments and how that state could reach a Deno isolate. Done means an agreed and documented mechanism that lets an application distinguish production from preview deployments as deployment status changes.

Written by the indexing model from the issue text.