Refactor metadata detector tool to add easily new file names to detect

The metadata detector detects at present only 'package.json' and 'codemeta.json': https://forge.softwareheritage.org/source/swh-indexer/browse/master/swh/indexer/metadata_detector.py

Find a way to add easily a new file name to detect to the list of file names according to the parsers available with the metadata translator.

Easy to add, hard to maintain.

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Migrated from T1235 (view on Phabricator)