[CodeMeta] Add checker that file is complete for citation

We need a flag that tells the user if the codemeta.json is complete and compliant for software citation.

1. see mandatory fields for citation
2. if not all -> show flag "Your codemeta.json file doesn't contain enough information to cite your software" Should this be part of the validation of the file ?

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Migrated from T2046 (view on Phabricator)