fix(api): revert removing index import for api plugin register file

This appears to be a small change that reverted a reverted commit but which broke the ambient
declaration merging of the api plugin. This change restores the api plugin to be consistent with the
various other plugins and to properly export the merged types again

Author: MrBazlow

packages/api/src/register.ts

@@ -1,3 +1,5 @@
+import './index';
+
 import { Plugin, postInitialization, preLogin, SapphireClient } from '@sapphire/framework';
 import type { ClientOptions } from 'discord.js';
 import { loadListeners, loadMiddlewares, loadRoutes, Server } from './index';