Default add DOMjudge team to admin user

[vmcj]

We already did this in development for ourselves. Because jury users can't import problems and we don't want that, this is the easiest fix.

Closes: https://github.com/DOMjudge/domjudge/issues/2152

@meisterT I know you had a different opinion in the issue but I think the code has changed since that discussion.