Turns out that using this method sometimes fails with an exception about unable to delete a directory.
The stacktrace points to:

```
java.nio.file.FileSystemException: /tmp/webwolf-fileserver/dumbanddummer/xxe_a11.dtd: Not a directory
        at java.base/sun.nio.fs.UnixException.translateToIOException(UnixException.java:100) ~[na:na]
        at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:106) ~[na:na]
        at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:111) ~[na:na]
        at java.base/sun.nio.fs.UnixFileSystemProvider.implDelete(UnixFileSystemProvider.java:248) ~[na:na]
        at java.base/sun.nio.fs.AbstractFileSystemProvider.deleteIfExists(AbstractFileSystemProvider.java:110) ~[na:na]
        at java.base/java.nio.file.Files.deleteIfExists(Files.java:1191) ~[na:na]
        at java.base/java.nio.file.Files.copy(Files.java:3147) ~[na:na]
        at io.undertow.server.handlers.form.FormData$FileItem.write(FormData.java:274) ~[undertow-core-2.3.10.Final.jar!/:2.3.10.Final]
        at io.undertow.servlet.spec.PartImpl.write(PartImpl.java:119) ~[undertow-servlet-2.3.10.Final.jar!/:2.3.10.Final]
        at org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile.transferTo(StandardMultipartHttpServletRequest.java:254) ~[spring-web-6.0.13.jar!/:6.0.13]
        at org.owasp.webgoat.webwolf.FileServer.importFile(FileServer.java:89)
```

It has to do with the underlying implmentation in Undertow. An explaination can be found here: https://stackoverflow.com/questions/60336929/java-nio-file-nosuchfileexception-when-file-transferto-is-called

The solution is to take the input stream and use a simple `Files.copy()` to copy the file.

Closes: #1737