turn all slash command replies into an ephemeral message

Setting ephemeral has to happen in an initial reply (reply() or
deferReply()) to set the mode for all replies in this 'thread'. Once the
ephemeral state of a message has been set it can not be changed. If you
want to send a visible message after an ephemeral message it has to be
new message. See https://discordjs.guide/slash-commands/response-methods.html#ephemeral-responses

server/events/interactionCreate.ts

@@ -8,7 +8,7 @@ export async function execute(interaction: ExtendedInteraction) {
   //console.dir(interaction, { depth: null })
   if (interaction.isCommand()) {
     logger.info(`Interaction is a command.`, { guildId: interaction.guild?.id })
-    await interaction.deferReply()
+    await interaction.deferReply({ ephemeral: true })
     const command = client.commands.get(interaction.commandName)
     if (!command)
       return interaction.followUp('Invalid command')