refactor(microservices): Extract AmqpExchangeType

Defined a dedicated type for AMQP exchange types to enhance type safety and maintain IDE support,
replacing inline union with a named type for better readability and reusability.

Author: ChangmoKang

packages/microservices/external/rmq-url.interface.ts

@@ -68,3 +68,10 @@ export interface AmqplibQueueOptions {
   maxPriority?: number;
   [key: string]: any;
 }
+
+type AmqpMainExchangeType = 'direct' | 'fanout' | 'topic' | 'headers';
+
+/**
+ * @publicApi
+ */
+export type AmqpExchangeType = AmqpMainExchangeType | (string & {});

packages/microservices/interfaces/microservice-configuration.interface.ts

@@ -14,6 +14,7 @@ import { MqttClientOptions, QoS } from '../external/mqtt-options.interface';
 import { IORedisOptions } from '../external/redis.interface';
 import {
   AmqpConnectionManagerSocketOptions,
+  AmqpExchangeType,
   AmqplibQueueOptions,
   RmqUrl,
 } from '../external/rmq-url.interface';
@@ -286,7 +287,7 @@ export interface RmqOptions {
      * Type of the exchange
      * @default 'topic'
      */
-    exchangeType?: string;
+    exchangeType?: AmqpExchangeType;
     /**
      * Additional routing key for the topic exchange.
      */