Fix name resolve for nested models.

[Vasiliy566]

@aminalaee sorry for that - somehow this commit missed in previous request, require this for nested models - please release it.

[Vasiliy566]

previous pr - https://github.com/aminalaee/sqladmin/pull/829 now it works only for models that dont links to another, this fix allow json export for all models.

[aminalaee]

That's ok, but please update the tests so we know the fix is working.

[Vasiliy566]

@aminalaee done