feat(gateway): add plugin host module

apps/gateway/src/plugin/plugin.service.ts

@@ -0,0 +1,16 @@
+import { Inject, Injectable } from '@nestjs/common';
+import { PLUGIN_REGISTRY } from './plugin.module.js';
+import type { IChannelPlugin } from './plugin.interface.js';
+
+@Injectable()
+export class PluginService {
+  constructor(@Inject(PLUGIN_REGISTRY) private readonly plugins: IChannelPlugin[]) {}
+
+  getPlugins(): IChannelPlugin[] {
+    return this.plugins;
+  }
+
+  getPlugin(name: string): IChannelPlugin | undefined {
+    return this.plugins.find((plugin: IChannelPlugin) => plugin.name === name);
+  }
+}