Add confirmation step to Join Event button in Slack

[danieltott]

When joining our Co-Working Room, users are prompted with a nice confirmation step:

It would be great to add this to our Join Event slack buttons.

The co-working room prompt is contained in the button accessory - you can see that here:

webhooks/functions/zoom-meeting-webhook-handler/slack.js

Lines 23 to 53 in 3536649

	accessory: {
	type: 'button',
	text: {
	type: 'plain_text',
	text: timestamp ? room.ButtonStartNew : room.ButtonJoin,
	emoji: true,
	},
	value: 'join_meeting',
	url: room.ZoomMeetingInviteUrl,
	action_id: 'button-action',
	style: 'primary',
	confirm: {
	title: {
	type: 'plain_text',
	text: room.NoticeTitle,
	},
	text: {
	type: 'mrkdwn',
	text: room.NoticeBody,
	},
	confirm: {
	type: 'plain_text',
	text: room.NoticeConfirm,
	},
	deny: {
	type: 'plain_text',
	text: room.NoticeCancel,
	},
	},
	},
	},

Here's the accessory button for the Join Event message:

webhooks/functions/event-reminders-hourly/index.js

Lines 128 to 134 in 3536649

	titleBlock.accessory = {
	type: 'button',
	text: {
	type: 'plain_text',
	text: 'Join Event',
	emoji: true,
	},

The message text for the coworking room is:

Heads up!

This is a Zoom link - following it will most likely open Zoom and add you to our Co-Working Room.
Additionally, as always, our [Code of Conduct](https://virtualcoffee.io/code-of-conduct) is in effect.
Just want to make sure we're all on the same page :smiley:

However, not all of our events are Zoom links. So we could either just make this much more generic ("this is an external link...") or try to parse the event url and add some options canned options (Zoom, twitch, etc) plus a generic fallback.