Generate mw/core doxygen on new release

Add mediawiki-core-doxygen-publish to the `publish` pipeline which
should generate doxygen documentation for a new MediaWiki release.

Adjust the job branch: filter to accept tags ref-updates events
according to source code https://review.openstack.org/14096

Change-Id: I90f044ea78c1f87cd1720ace04c63ccbc88a7a41