Remove StringLength attributes from Entities

[Masterjun3]

This PR removes the string length attributes and makes an empty migration, only changing the model snapshot.

We use postgres columns text (or rather citext) which doesn't have string limits.
And we don't need a limited string type, as per the docs:

While character(n) has performance advantages in some other database systems, there is no such advantage in PostgreSQL; in fact character(n) is usually the slowest of the three because of its additional storage costs. In most situations text or character varying should be used instead.

I haven't found any uses of direct Entity types for form binding (this would cause client and server validation to be removed by this PR). We basically always use a separate model for that.
Those models now technically don't need the StringLength either, but even though we can store any lenghts, we still don't need to allow users to spam us with massive strings.