Update createMessage tag to indicate 1024 limit
Update createMessage tag to indicate 1024 limit

Per https://trello.com/c/aLOI7spB/56-tag-parameter-character-limit-is-1024-for-v2, this change adds the notice of a 1024 character limit on the 'tag' field in V2 message sending.

dtolb/v2-messaging,dtolb/v2-messaging,dtolb/v2-messaging