Needed changes for HS 1.21 release

[zhiyuli]

This is a running list

1. a new bool parameter "validate_url_flag" added to endpoint for RefFileType creation to specify whether to validate url. (changes needed on both HS and hs_restclient)
   {url_base}/resource/data-store-add-reference/

2) update extra_metadata (no change on HS side; taken care of in hs_restclient 1.20)

3. get extra_metadata (changes needed on both HS and hs_restclient)