Unable to distinguish tail message type from the websocket message payload

### What version of `Wrangler` are you using?

0.0.0

### What operating system are you using?

Mac

### Describe the Bug

(sent here from the #do-alarms Discord channel by Matt @ cloudflare)

Please add a new field to every tail websocket wire protocol message to distinguish the various contexts now present in workers. Right now it is impossible to always tell the difference between eyeball requests, DO requests, cron requests, and now DO alarm requests [*].

Could be a type code number if necessary to keep the payload small.

Would be immediately useful, thanks! I don't use wrangler, but use the WS directly.

\* strictly speaking cron requests can be identified by the payload properties, but the others are often ambiguous