[manual] send_message: Rename recipient/stream fields to 'to'.

This commit changes APIs and requires and update of all zephyr
mirroring bots to deploy properly.

(imported from commit 2672d2d07269379f7a865644aaeb6796d54183e1)

bots/feedback-bot

@@ -19,7 +19,7 @@ def forward_message(message):
         return
     forwarded_message = {
         "type": "stream",
-        "stream": "support",
+        "to": "support",
         "subject": "feedback from %s" % message["sender_email"],
         "content": message["content"],
         }