Add a field _metadataDirectory

[twagoo]

To allow for the implementation of clarin-eric/curation-dashboard#13, add a field that is populated with the relative path of the directory containing the CMDI file. This would be a substring of the value of _fileName. Example:

{
        "_fileName":"/srv/vlo-data/clarin/results/cmdi/HZSK_Repository/oai_corpora_uni_hamburg_de_spoken_corpus_demo.xml",
        "_metadataDirectory":"clarin/results/cmdi/HZSK_Repository"
}

An example query via URL would be:

• /search?q=_metadataDirectory:%22clarin/results/cmdi/HZSK_Repository%22

Note that the following is already possible but in theory it is not 100% reliable and not optimised for performance:

• /search?q=_fileName:*clarin/results/cmdi/HZSK_Repository*