Update defcustom type for hui-mini menus

[matsl]

What

Update defcustom type for hui-mini menus so that customize works. Extra bonus removes warnings about not valid type.

Why

I noted the following warnings for the master build.

hui-mini.el:941:12: Warning: in defcustom for `hui:menu-rolo': `nil' is not a valid type
hui-mini.el:971:12: Warning: in defcustom for `hui:menu-to': `nil' is not a valid type
hui-mini.el:1010:12: Warning: in defcustom for `hui:doc-a-z': `nil' is not a valid type

That led me to try to use the defcustom for these menues and they were broken. I have verified with 27.2 that the defcustom works as expected after this change.

Q: Do we want to have these menus customizable? (Using customize for long and complicated expressions feels to me like a bad interface. Would you as a user not prefer to define the menu a lisp expression!?)

Note

Different warnings from native run and docker run

Interesting thing is that we are getting a few warnings when we build using the docker images that I don't see when building natively on my machine. I do not get these. I have no idea why. Is it because I run a local emacs that has native compilation!? When I run in docker locally I get the same warnings as in CI/CD which is expected.

hui:doc-a-z

This menu is a little complicated since it also have items that does not have an sexp. See the the last "" selection. From the editing perspective it seems like setting the sexp to nil works and the default value is displayed properly. So this menu might benefit from another type definition.