Validate the presence of default User and UserPreference attributes

What does this MR do and why?

This is a follow-up of !102897 (diffs).

We want to make the columns with defaults NOT NULL in our database. As the first step according to our database guidelines, we want to validate their presence in the models.

MR	Step
Validate the presence of default User and UserP... (!125728 - merged)	1 👈 You are here
Prevent adding new records with null attributes (!125744 - merged)	2
Fill null values of user_preferences table with... (!125774 - merged)	3

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Related to #388393 (closed)