Save new users' region_id (now we save forum folder id)

In every region there are several folders on the forum.
in the beginning the 'regional" logic was based on id of each specific folder.
But now we found out the the list of folders inside a region – is dynamic.

so we'd need to start saving not only region folder id, but also region_id to database – as user preference. I've created a dedicated table, which we'd need to update accordingly when user set / modified their list of regions.

Current "source of truth" about user's choice of regions – is the table `user_regional_preferences`.
Goal of this Issue – is to start updating table `user_pref_region` for all regions in parallel to `user_regional_preferences`. (in future we'll deactivate `user_regional_preferences`)
NB 1, we already updating this table ONLY for Moscow region in function `manage_if_moscow` – as a test it works.
NB 2, in addition of adding regions into `user_pref_region` we need to develop a mechanism of deleting of records form there if user changes their region.