Add Select menu to ban modal's message deletion length field

[saramaebee]

mod-bot/src/commands/ban.ts

Lines 26 to 30 in 3c3f469

	new TextInputBuilder()
	.setCustomId("banLength")
	.setLabel("How far back should we delete messages?")
	.setStyle(TextInputStyle.Short)
	]

Currently, we're just using a text field, as discord.js doesn't support select fields in modals yet. We can hack around this by making raw API requests to Discord.