Refactor to more consistent structure (e.g. "plugins")

plugins/ping.ts

@@ -0,0 +1,22 @@
+import {SlashCommandBuilder} from 'discord.js';
+
+import {BasePlugin, type Settings} from '../plugin';
+
+export class PingPlugin extends BasePlugin {
+	constructor(settings: Settings) {
+		super(settings);
+		this.commands = [
+			{
+				data: new SlashCommandBuilder()
+					.setName('ping')
+					.setDescription('Send a ping to the bot'),
+
+				execute: async interaction => {
+					await interaction.reply(
+						`Pong! This command was run by ${interaction.user.username}, who joined on ${interaction.member?.joinedAt}.`,
+					);
+				},
+			},
+		];
+	}
+}