Add channel_id_changed event

[stevengill]

Description

Payload:

"event": {
  "type": "channel_id_changed",
  "old_channel_id": "G012Y48650T",
  "new_channel_id": "C012Y48650T",
  "event_ts": "1612206778.000000"
},

Should be launching on 02/08

What type of issue is this? (place an x in one of the [ ])

• enhancement (feature request)

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.