Update repository workflow file (count unavailable files)

[yasandu0505]

• Since we have decided to remove the unavailable.txt files from the file system. then we come up with a issue on the workflow , because it calculates the unavailable documents by counting those files unavailable.txt files.

• We have to upgrade the workflow to count the unavailable documents by reading the metadata.json files and count the documents where the
  document_type == 'UNAVAILABLE'