feature: Support Gateway Intents (#1566)

* Support Gateway Intents

Allows supplying gateway intents through DiscordSocketConfig which will be passed through the IDENTIFY payload, in order to choose what gateway events you want to receive.

* Fixing enum casing

* Feedback

* Updating comment for GuildSubscriptions

* Comment update

src/Discord.Net.WebSocket/API/Gateway/IdentifyParams.cs

@@ -1,4 +1,4 @@
-#pragma warning disable CS1591
+#pragma warning disable CS1591
 using Newtonsoft.Json;
 using System.Collections.Generic;
 
@@ -17,5 +17,7 @@ namespace Discord.API.Gateway
         public Optional<int[]> ShardingParams { get; set; }
         [JsonProperty("guild_subscriptions")]
         public Optional<bool> GuildSubscriptions { get; set; }
+        [JsonProperty("intents")]
+        public Optional<int> Intents { get; set; }
     }
 }