Add 'DNS Zone Settings' implementation

src/Extensions/Cloudflare.Dns/Models/DnsZoneInternalDns.cs

@@ -0,0 +1,14 @@
+namespace AMWD.Net.Api.Cloudflare.Dns
+{
+	/// <summary>
+	/// Settings for this internal zone.
+	/// </summary>
+	public class DnsZoneInternalDns
+	{
+		/// <summary>
+		/// The ID of the zone to fallback to.
+		/// </summary>
+		[JsonProperty("reference_zone_id")]
+		public string? ReferenceZoneId { get; set; }
+	}
+}