Update required media item fields
Update required media item fields

As of https://gerrit.wikimedia.org/r/#/c/436360/ (adding support for
Mathoid images) media items may not have the usual set of Commons
metadata.  This updates the media spec to fix the monitoring check.

wikimedia/mediawiki-services-restbase,d00rman/restbase,cscott/restbase,milimetric/restbase,d00rman/restbase,wikimedia/mediawiki-services-restbase,Pchelolo/restbase,Pchelolo/restbase,wikimedia/restbase,cscott/restbase,milimetric/restbase,wikimedia/restbase