feature: Add INVITE_CREATE and INVITE_DELETE events (#1491)

* Add invite events (create and delete)

* Removed unused using

* Fixing IInviteMetadata properties

* Add two new fields to the gateway event

* Better event summary and remarks

* Change how to assign to target variable

Co-Authored-By: Joe4evr <jii.geugten@gmail.com>

* Applying suggested changes to TargetUserType

* Renaming NotDefined to Undefined

* Fixing xml docs

* Changed the summary style format

Co-authored-by: Joe4evr <jii.geugten@gmail.com>

src/Discord.Net.WebSocket/BaseSocketClient.Events.cs

@@ -389,5 +389,47 @@ namespace Discord.WebSocket
             remove { _recipientRemovedEvent.Remove(value); }
         }
         internal readonly AsyncEvent<Func<SocketGroupUser, Task>> _recipientRemovedEvent = new AsyncEvent<Func<SocketGroupUser, Task>>();
+
+        //Invites
+        /// <summary>
+        ///     Fired when an invite is created.
+        /// </summary>
+        /// <remarks>
+        ///     <para>
+        ///         This event is fired when an invite is created. The event handler must return a
+        ///         <see cref="Task"/> and accept a <see cref="SocketInvite"/> as its parameter.
+        ///     </para>
+        ///     <para>
+        ///         The invite created will be passed into the <see cref="SocketInvite"/> parameter.
+        ///     </para>
+        /// </remarks>
+        public event Func<SocketInvite, Task> InviteCreated
+        {
+            add { _inviteCreatedEvent.Add(value); }
+            remove { _inviteCreatedEvent.Remove(value); }
+        }
+        internal readonly AsyncEvent<Func<SocketInvite, Task>> _inviteCreatedEvent = new AsyncEvent<Func<SocketInvite, Task>>();
+        /// <summary>
+        ///     Fired when an invite is deleted.
+        /// </summary>
+        /// <remarks>
+        ///     <para>
+        ///         This event is fired when an invite is deleted. The event handler must return
+        ///         a <see cref="Task"/> and accept a <see cref="SocketGuildChannel"/> and
+        ///         <see cref="string"/> as its parameter.
+        ///     </para>
+        ///     <para>
+        ///         The channel where this invite was created will be passed into the <see cref="SocketGuildChannel"/> parameter.
+        ///     </para>
+        ///     <para>
+        ///         The code of the deleted invite will be passed into the <see cref="string"/> parameter.
+        ///     </para>
+        /// </remarks>
+        public event Func<SocketGuildChannel, string, Task> InviteDeleted
+        {
+            add { _inviteDeletedEvent.Add(value); }
+            remove { _inviteDeletedEvent.Remove(value); }
+        }
+        internal readonly AsyncEvent<Func<SocketGuildChannel, string, Task>> _inviteDeletedEvent = new AsyncEvent<Func<SocketGuildChannel, string, Task>>();
     }
 }