Add an Interaction Response Type to delete message

[A5rocks]

Sometimes people need to delete the message a component was on. However, there is no good way to do this.

At the moment I can think of three work-arounds, all flawed:

• Use a bot account to delete the message.
  This does not work because not every application using interactions has a bot account.
• Store the interaction token for the old message.
  Requires state + tokens expire.
• Respond with type 6 or 7, and then use the delete original message route.
  This is subobtimal for a couple reasons:
  • Not guaranteed by Discord. Just like how type 4/5 don't work for this, Discord could break 6/7 at any time. I am told that actually, this is guaranteed.
  • It leaves an ugly remnant -- followup messages are "in reply to" a deleted message.
  • Feels like a weird hack, and requires some thought to think of

Instead of using those, having a dedicated response type for this would easily solve this problem.