Version >= 11:
Settings -> Code Style -> Java -> Imports (tab)
.
Version < 11
Settings -> Code Style -> Imports
In the middle of the pane is the "Packages to Use Import with '*'" table. You can add an entry here of a fully-qualified class name, and tick the static box; now all static methods in this class will be available for auto-completion.
(I'm not sure how the static import works with specifying a package, as I've never tried it, but I don't see why it wouldn't. Specifying a super-package and ticking the "with subpackages" option could be even more interesting.)
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