suggestion: generate Telegram webhook secret token on Tranquil startup

While setting up the Telegram communication channel, I noticed that Tranquil required to configure a webhook secret token, and was a bit confused on why it did, as usually applications manage that themselves once they have the bot token.

Since you're already setting the Telegram webhook URL yourselves with TelegramSender::set_webhook, you can generate a webhook secret on-the-fly and pass it across the application instead of requiring it to be configured manually via the telegram.webhook_secret configuration option.

This would make configuration simpler, and also prevent administrator error, in case they don't understand how Telegram webhooks work and set that value to a secret another bot of theirs is already using.