Add support for extracting channels from data dump in exportall

Closes #597

DiscordChatExporter.Cli/Commands/GetDirectChannelsCommand.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Infrastructure;
+using DiscordChatExporter.Cli.Commands.Base;
+using DiscordChatExporter.Core.Discord.Data;
+using DiscordChatExporter.Core.Utils.Extensions;
+
+namespace DiscordChatExporter.Cli.Commands;
+
+[Command("dm", Description = "Get the list of direct message channels.")]
+public class GetDirectChannelsCommand : DiscordCommandBase
+{
+    public override async ValueTask ExecuteAsync(IConsole console)
+    {
+        var cancellationToken = console.RegisterCancellationHandler();
+
+        var channels = (await Discord.GetGuildChannelsAsync(Guild.DirectMessages.Id, cancellationToken))
+            .Where(c => c.Kind != ChannelKind.GuildCategory)
+            .OrderByDescending(c => c.LastMessageId)
+            .ThenBy(c => c.Name)
+            .ToArray();
+
+        foreach (var channel in channels)
+        {
+            // Channel ID
+            await console.Output.WriteAsync(
+                channel.Id.ToString().PadRight(18, ' ')
+            );
+
+            // Separator
+            using (console.WithForegroundColor(ConsoleColor.DarkGray))
+                await console.Output.WriteAsync(" | ");
+
+            // Channel category / name
+            using (console.WithForegroundColor(ConsoleColor.White))
+                await console.Output.WriteLineAsync($"{channel.Category.Name} / {channel.Name}");
+        }
+    }
+}