This PR adds a new "Pause notifications" checkbox to the user status modal. This checkbox allows enabling the Do-Not-Disturb mode together with user status. Note that we don't remove and don't rename the existing DnD menu item in this PR, so the old way of entering the DnD mode is still available.
Also, we're not making DnD mode a part of user status on backend and in database. The reason is that the DnD mode should still be available on sites with disabled user status, having them separated helps keep the implementation simple.
User options were serialized at the root level of CurrentUserSerializer,
but UserSerializer has a user_option field. This inconsistency caused
issues in the past because user_option fields had to be duplicated on
the frontend.
This reverts commit 94c3bbc2d1.
At this current point in time, we do not have enough data on whether
this centralisation is the trade-offs of coupling features into a single
channel.
