Make UnpackContent recognize tar mime type from DetectMimeType

While creating a pipeline using a DetectMimeType and UnpackContent processor, I noticed that the UnpackContent expects application/tar inside of the mime.attribute for tar archives, which is not correct. The Apache Tika project actually produces (1) application/x-tar.

(1): https://tika.apache.org/1.11/api/org/apache/tika/server/writer/TarWriter.html

This fix should be fairly simple. I propose we modify the UnpackContent processor to accept both application/tar and application/x-tar to ensure backwards compatibility with previous workflows.