chore: add close method on multi region cache client (#15)

Closes connections on the enclosed clients.

src/IMultiRegionCacheWriterClient.ts

@@ -54,4 +54,6 @@ export interface IMultiRegionCacheWriterClient {
       | Array<[string, number]>,
     options?: SortedSetPutElementsOptions
   ): Promise<MultiRegionCacheSortedSetPutElements.Response>;
+
+  close(): void;
 }

src/multi-region-cache-writer-client.ts

@@ -172,6 +172,15 @@ export class MultiRegionCacheWriterClient
   public get configuration(): Configuration {
     return this._configuration;
   }
+
+  /**
+   * Closes all the enclosed cache clients.
+   */
+  public close(): void {
+    for (const client of Object.values(this.clients)) {
+      client.close();
+    }
+  }
 }
 
 function getDefaultCacheClientConfiguration(): Configuration {