Adds typing notification constants to the response given by
`POST /register`. Until now, these were hardcoded by clients
based on the documentation for implementing typing notifications
in the main endpoint description for `api/set-typing-status`.
This change also reflects updating the web-app frontend code
to use the new constants from the register response.
Co-authored-by: Samuel Kabuya <samuel.mwangikabuya@kibo.school>
Co-authored-by: Wilhelmina Asante <wilhelmina.asante@kibo.school>