Improve docs, add missing dispose

Author: Leo

FirebaseAdmin/FirebaseAdmin/Messaging/FirebaseMessaging.cs

@@ -319,7 +319,7 @@ public async Task<BatchResponse> SendMulticastAsync(
         /// </summary>
         /// <param name="topic">The topic name to subscribe to. /topics/ will be prepended to the topic name provided if absent.</param>
         /// <param name="registrationTokens">A list of registration tokens to subscribe.</param>
-        /// <returns>The response produced by FCM topic management operations.</returns>
+        /// <returns>A task that completes with a <see cref="TopicManagementResponse"/>, giving details about the topic subscription operations.</returns>
         public async Task<TopicManagementResponse> SubscribeToTopicAsync(string topic, List<string> registrationTokens)
         {
             return await this.instanceIdClient.SubscribeToTopicAsync(topic, registrationTokens);
@@ -330,7 +330,7 @@ public async Task<TopicManagementResponse> SubscribeToTopicAsync(string topic, L
         /// </summary>
         /// <param name="topic">The topic name to unsubscribe from. /topics/ will be prepended to the topic name provided if absent.</param>
         /// <param name="registrationTokens">A list of registration tokens to unsubscribe.</param>
-        /// <returns>The response produced by FCM topic management operations.</returns>
+        /// <returns>A task that completes with a <see cref="TopicManagementResponse"/>, giving details about the topic unsubscription operations.</returns>
         public async Task<TopicManagementResponse> UnsubscribeFromTopicAsync(string topic, List<string> registrationTokens)
         {
             return await this.instanceIdClient.UnsubscribeFromTopicAsync(topic, registrationTokens);
@@ -342,6 +342,7 @@ public async Task<TopicManagementResponse> UnsubscribeFromTopicAsync(string topi
         void IFirebaseService.Delete()
         {
             this.messagingClient.Dispose();
+            this.instanceIdClient.Dispose();
         }
     }
 }

FirebaseAdmin/FirebaseAdmin/Messaging/InstanceIdClient.cs

@@ -70,7 +70,7 @@ public InstanceIdClient(HttpClientFactory clientFactory, GoogleCredential creden
     /// </summary>
     /// <param name="topic">The topic name to subscribe to. /topics/ will be prepended to the topic name provided if absent.</param>
     /// <param name="registrationTokens">A list of registration tokens to subscribe.</param>
-    /// <returns>The response produced by FCM topic management operations.</returns>
+    /// <returns>A task that completes with a <see cref="TopicManagementResponse"/>, giving details about the topic subscription operations.</returns>
     public async Task<TopicManagementResponse> SubscribeToTopicAsync(string topic, List<string> registrationTokens)
     {
         try
@@ -92,7 +92,7 @@ public async Task<TopicManagementResponse> SubscribeToTopicAsync(string topic, L
     /// </summary>
     /// <param name="topic">The topic name to unsubscribe from. /topics/ will be prepended to the topic name provided if absent.</param>
     /// <param name="registrationTokens">A list of registration tokens to unsubscribe.</param>
-    /// <returns>The response produced by FCM topic management operations.</returns>
+    /// <returns>A task that completes with a <see cref="TopicManagementResponse"/>, giving details about the topic unsubscription operations.</returns>
     public async Task<TopicManagementResponse> UnsubscribeFromTopicAsync(string topic, List<string> registrationTokens)
     {
         try