We immediately navigate the user to the conversation they just
sent a message to if they are not already in the appropriate
conversation view.
This commit adds a first-time banner to explain the same.
Fixes#29575.
Removes the 'onboarding_steps' field on 'UserProfile'
model which is no longer used.
It was introduced back in 2013 (b5e22bf), and is no
longer used.
Fixes part of #30043.