Search: Allow searching by md5, possibly UNF from UI

[kcondon]

This ticket is mostly in response to trying to find a duplicate MD5 within a dataset whose file has a different name but may or may not be generally useful, see #3129 , #2467

There is already a way to search from a URL for an md5 but not obvious to an end user: https://dataverse.harvard.edu/dataverse/harvard?q=fileMd5:48a76222cf5c06cb4f2d8f75cc0caa63 , from ticket #2038