create origin_metadata_translation

• storage.py (as the entry point of storage) add, get
• db.py (as the entry point to db)
• swh-func.sql (the actual sql procedure)
• add the table itself to swh-schema.sql and constraints to swh-indexes.sql
• the data about the indexer tool into swh-data.sql
• swh.storage.api.{server,client}
• tests for origin_metadata_translation

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Migrated from T795 (view on Phabricator)