Notify Discord channel on Raid Completion

[nobrayner]

• Update newRaid to send a message to "current raids" discord channel when a new raid is created: Send Webhook Message
  • Add a discordMessageId to raid stats document: will need to use the wait query parameter
• [x] Update completeRaid to:
  • Delete message from "current raids" channel using the discordMessageId: Delete Webhook Message
  • [x] Send message to "completed raids" channel

For what it's worth, I already created some TS types for sending a Discord webhook for a little GH action I made a while back: https://github.com/nobrayner/discord-webhook/blob/master/src/helpers/discordTypes.ts

[nobrayner]

This would benefit from #18, but really needs #7 so that there are sensical titles and metadata to use in the creation/other template.