FIX: avoid race condition when setting user status (#19817)

We caught it in logs, race condition led to this error:

    ActiveRecord::RecordNotUnique 
    (PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "user_statuses_pkey"
    DETAIL:  Key (user_id)=(15) already exists.)


The reason the problem happened was that we were checking if a user has status and if not inserting status:

    if user_status
      ...
    else
      self.user_status = UserStatus.create!(status)
    end

The problem is that it's possible that another request will insert status just after we check if status exists and just before our request call `UserStatus.create!(status)`. Using `upsert` fixes the problem because under the hood `upsert` generates the only SQL request that uses "INSERT ... ON CONFLICT DO UPDATE". So we do everything in one SQL query, and that query takes care of resolving possible conflicts.

app/models/user.rb

@@ -1790,14 +1790,17 @@ class User < ActiveRecord::Base
   end
 
   def set_status!(description, emoji, ends_at = nil)
-    status = { description: description, emoji: emoji, set_at: Time.zone.now, ends_at: ends_at }
-
-    if user_status
-      user_status.update!(status)
-    else
-      self.user_status = UserStatus.create!(status)
-    end
+    status = {
+      description: description,
+      emoji: emoji,
+      set_at: Time.zone.now,
+      ends_at: ends_at,
+      user_id: id,
+    }
+    validate_status!(status)
+    UserStatus.upsert(status)
 
+    reload_user_status
     publish_user_status(user_status)
   end
 
@@ -2175,6 +2178,10 @@ class User < ActiveRecord::Base
       )
     SQL
   end
+
+  def validate_status!(status)
+    UserStatus.new(status).validate!
+  end
 end
 
 # == Schema Information