Index CITATION.cff files

See description of metadata workflow here: https://www.softwareheritage.org/2019/05/28/mining-software-metadata-for-80-m-projects-and-even-more/

Here is the documentation about that https://docs.softwareheritage.org/devel/swh-indexer/metadata-workflow.html#adding-support-for-additional-ecosystem-specific-metadata

Migrated from T3078 (view on Phabricator)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information