Consider a "zero config" plugin architecture

[afischer]

Problem Description

It's currently somewhat cumbersome to add customizations to Library. People have used Docker-based solutions, or simply forked the repo in order to more easily get customizations added to the app.

Feature

It would be nice to add a more simple way to distribute and add plugins to Library. A few possibilities

• A config.yaml or customizations.yaml that allowed you to pass URLs of github gists that include middleware
• A plugin API and naming pattern (e.g. library-plugin-foo or @your-scope/library-plugin-foo) that automatically configured itself when installed alongside library, similar to how Parcel handles plugins.

[afischer]

Somewhat related to https://github.com/nytimes/library/issues/146