This allows setting a settings attrset in the module, which will then
change that setting to the specified value. This is particularly useful
for e.g. the `entryPage` setting, which you can then make set to a
particular value.
There's an escape hatch for string-valued secrets which live in the
settings, like the Steam API key: string-valued settings can be
specified by using the __FILE suffix on the setting name (e.g.
steamAPIKey__FILE) and then specifying the path to a file instead.
The content of that file will be used as the setting instead.
