makers.utils undocumented online

[Tobychev]

Gammapy version
0.18.2

Bug description
make_theta_squared_table docstring does not show up in the documentation search, and I can't find it via the menu either. Probably applies for all functions in that subpackage, but I haven't checked.

The function has a proper docstring, it's just not been caught during generation of the html page, and is thus hard to discover.

To Reproduce
Go to docs.gammapy.org and search for make_theta_squared_table, the only hit is in an example.

[github-actions]

Merci! We will respond to your issue shortly. In the meantime, try import gammapy; gammapy.song()

[registerrier]

Note that it appears in hess tutorials.

[bkhelifi]

I will add it in the PR about the missing links into the documentation