[Improvement] User-supplied install config

[adam-alchemy]

• Currently the spec supports dependencies and injected hooks. These address two problems with using plugin manifests alone:
  • Dependencies address “plugin incompatibilities”, where a plugin needs external functionality that it doesn’t want to hard-code. Right now this is only used for providing owner/root validation functions for sensitive plugin functions.
  • Injected hooks address “plugin permissions” by providing a way to apply protective checks to plugins as they’re installed, providing guard rails that “limit the blast radius” of malicious plugins. This can’t be done via regular plugin hooks for 2 reasons:
    • Manifests must be static in their contents, which means you would need a different manifest to apply a “permission” hook to different plugins. And since manifests are static, this means re-compiling the permissions plugin for each other plugin it is providing checks for.
    • Hooks must be applied after the plugin is installed, and unfortunately onInstall would allow a malicious plugin to perform actions before its permissions plugin is installed.
• These are very opinionated usages, and the specifics of how they are used bleeds into the standard itself. If we can generalize “user supplied install configs” as a mechanism to supplement or override manifest fields, we can reduce spec complexity.

[jaypaik]

Related: #22, which proposes removal of injected hooks.