Function `probnum.diffeq.odefilter.utils.ivp_to_regression_problem` is not displayed in the docs

[pnkraemer]

Describe the bug
The function probnum.diffeq.odefilter.utils.ivp_to_regression_problem is not displayed in the docs. (The entire odefilter.utils bit does not exist). But it should.

I am talking about this function:
https://github.com/probabilistic-numerics/probnum/blob/main/src/probnum/diffeq/odefilter/utils/_problem_utils.py

And I would like the odefilter.utils appear next to init_routines, information_operators, etc.:
https://probnum.readthedocs.io/en/latest/api/diffeq/odefilter.html