One time setup code for all deployments

It would be nice to have a way to only execute a setup code once when it's deployed, instead of every time the route is called.

For example, when building Discord bot with slash commands, we usually have the code to register those commands with Discord first. At the moment, we need to do the registration step somewhere else (the example shows using `curl`) and only take the Deno Deploy server handle interaction requests.

Being able to also do the registration in the Deploy code keeps the list of commands consistent and in one place.

The issue names no files, tests, or entry points. Start by locating how Deno Deploy handles application startup and route requests, then determine how a deployment-scoped setup hook would run once while keeping Discord command registration in the same codebase; done means setup does not repeat on each request.

Written by the indexing model from the issue text.