Cannot define global Nest providers in plugins

[michaelbromley]

Describe the bug
In Nest, you can define global providers such as interceptors like this:

@Module({
  providers: [
    {
      provide: APP_INTERCEPTOR,
      useClass: LoggingInterceptor,
    },
  ],
})
export class AppModule {}

Moreover, this should be possible from any module:

you can set up an interceptor directly from any module
source

Since Vendure plugins are a superset of Nest modules, it should also be possible to define these global providers from plugins. However, currently they do not work due to this part of the plugin-handling code:

vendure/packages/core/src/plugin/vendure-plugin.ts

Lines 131 to 141 in 98e463e

	const nestModuleMetadata = pick(pluginMetadata, Object.values(MODULE_METADATA) as any);
	// Automatically add any of the Plugin's "providers" to the "exports" array. This is done
	// because when a plugin defines GraphQL resolvers, these resolvers are used to dynamically
	// created a new Module in the ApiModule, and if those resolvers depend on any providers,
	// the must be exported. See the function {@link createDynamicGraphQlModulesForPlugins}
	// for the implementation.
	nestModuleMetadata.exports = [
	...(nestModuleMetadata.exports || []),
	...(nestModuleMetadata.providers || []),
	];
	Module(nestModuleMetadata)(target);

Attempting to define global providers will result in an error like:

[run:worker] error 22/04/21, 14:18 - [ExceptionHandler] Nest cannot export a provider/module that is not a part of the currently process
ed module (PluginWithGlobalProviders). Please verify whether the exported APP_INTERCEPTOR is available in this particular context.
[run:worker]
[run:worker] Possible Solutions:
[run:worker] - Is APP_INTERCEPTOR part of the relevant providers/imports within PluginWithGlobalProviders?

Expected behavior
Global providers should work as described in the Nest docs.

Environment (please complete the following information):

• @vendure/core version: 1.0.0-beta.8
• Nodejs version: any
• Database (mysql/postgres etc): any

Additional context
The fix is probably to inspect the providers array and filter out the following tokens: APP_INTERCEPTOR, APP_PIPE, APP_GUARD, APP_FILTER