[Feature] New ModifyCurrentApplication features (#2730)

* initial commit

* apply suggestings lol

* Update src/Discord.Net.Core/Entities/Applications/IApplication.cs

Co-authored-by: Quin Lynch <49576606+quinchs@users.noreply.github.com>

* check for null values inside the array

---------

Co-authored-by: Quin Lynch <49576606+quinchs@users.noreply.github.com>

src/Discord.Net.Core/DiscordConfig.cs

@@ -232,5 +232,10 @@ namespace Discord
         ///     Returns the max length of an application description.
         /// </summary>
         public const int MaxApplicationDescriptionLength = 400;
+
+        /// <summary>
+        ///     Returns the max amount of tags applied to an application.
+        /// </summary>
+        public const int MaxApplicationTagCount = 5;
     }
 }