By default `lib.evalModules` will check all config definitions match
a declared option (or a freeform type), leading to errors like:
error: The option `wrapRc' does not exist.
Setting `_module.freeformType` or `_module.check` will disable this,
allowing us to evaluate the option declaration without checking the
config definitions.
This commit only adds Home-Manager specific options, we should add
sections for the different kind of modules too.
This is _not_ added to the man docs, as it is more complex. If need
arises we could look into how to do it.
