[FEATURE]: Manage plugins like providers in configuration

[itlackey]

Feature hasn't been suggested before.

• [x] I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

It would be great to be able to override global plugin settings. This would work similar to providers to allow a default global set of plugins, but allow full control at a project level to customize what is available to that project. It could follow the same (or very similar) configuration pattern.

Global Configuration

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": ["@some/plugin", "@different/plugin"],
}

Project Configuration

{
  "$schema": "https://opencode.ai/config.json",
  "disabled_plugins": [
    "@some/plugin" // Overrides the global config and does not load this plugin
  ],
  "enabled_plugins": [
    "@project/plugin",
    "@different/plugin" //Optional since already in global config
  ]
}