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.Core/Entities/Invites/TargetUserType.cs

@@ -0,0 +1,14 @@
+namespace Discord
+{
+    public enum TargetUserType
+    {
+        /// <summary>
+        ///     The invite whose target user type is not defined.
+        /// </summary>
+        Undefined = 0,
+        /// <summary>
+        ///     The invite is for a Go Live stream.
+        /// </summary>
+        Stream = 1
+    }
+}