fix: Sending 2 requests instead of 1 to create a Guild role. (#1557)

The GuildHelper.CreateRoleAsync() was sending 2 requests to create a role. One to create the role, and one to modify the role that was created. This can be done in one request. So i have moved it to a single request to lower the amount of requests send to the api. This will also solve issue #1451.

src/Discord.Net.Rest/API/Rest/CreateGuildRoleParams.cs

@@ -0,0 +1,19 @@
+using Newtonsoft.Json;
+
+namespace Discord.API.Rest
+{
+    [JsonObject(MemberSerialization = MemberSerialization.OptIn)]
+    public class CreateGuildRoleParams
+    {
+        [JsonProperty("name")]
+        public Optional<string> Name { get; set; }
+        [JsonProperty("permissions")]
+        public Optional<ulong> Permissions { get; set; }
+        [JsonProperty("color")]
+        public Optional<uint> Color { get; set; }
+        [JsonProperty("hoist")]
+        public Optional<bool> Hoist { get; set; }
+        [JsonProperty("mentionable")]
+        public Optional<bool> Mentionable { get; set; }
+    }
+    }