(#23403) 'autosign' setting should manage file parameters

Puppet settings of type :file can specify the owner, group, and mode of
the file specified by the setting, like so:

    [master]
    autosign = $confdir/autosign.conf { mode = 664, owner = service, group = service}

Commit bca628dc extracted the autosign setting validation to a setting
class but dropped the ability for file settings to be specified. This
commit resolves the issue by making the autosign setting inherit from
the file setting.
(#23403) Do File.expand_path on the expected path

The FileSetting#to_resource method will call File.expand_path, which on
Windows, will convert a relative path like /foo/bar to an absolute path based
on the current drive.

This commit changes to the test so that the autoconf setting returns an
absolute path.
Merge branch 'pr/2150' into stable

* pr/2150:
  (#23403) Do File.expand_path on the expected path
  (#23403) 'autosign' setting should manage file parameters