feat(GuildManager): add AFK and system channel options in create (#4837)

This commit adds support for the `afk_channel_id`, `afk_timeout`, and
`system_channel_id` parameters in the
[create guild](https://discord.com/developers/docs/resources/guild#create-guild-json-params)
endpoint by adding the `afkChannelID`, `afkTimeout`, and
`systemChannelID` options in `GuildManager#create`.

This commit also fixes a minor bug in `create` when specifying types for
the channels due to the channel types not being changed from `'text'`,
`'voice'` etc to the corresponding numbers, so Discord would return an
error.

test/createGuild.js

@@ -0,0 +1,31 @@
+'use strict';
+
+const assert = require('assert');
+const { token } = require('./auth');
+const { Client } = require('../src');
+
+const client = new Client();
+
+client.on('ready', async () => {
+  try {
+    const guild = await client.guilds.create('testing', {
+      channels: [
+        { name: 'afk channel', type: 'voice', id: 0 },
+        { name: 'system-channel', id: 1 },
+      ],
+      afkChannelID: 0,
+      afkTimeout: 60,
+      systemChannelID: 1,
+    });
+    console.log(guild.id);
+    assert.strictEqual(guild.afkChannel.name, 'afk channel');
+    assert.strictEqual(guild.afkTimeout, 60);
+    assert.strictEqual(guild.systemChannel.name, 'system-channel');
+    await guild.delete();
+    client.destroy();
+  } catch (error) {
+    console.error(error);
+  }
+});
+
+client.login(token).catch(console.error);