create indexing strategy for metadata

==Metadata component design and implementation with indexing strategy== This is only for a first syntactic approach for intrinsic metadata with a fish for file names listed in swh/meta$152 and parse content to json

===Note: === In a later task will be to implement semantic translation of intrinsic metadata where the translation will be stored in a higher level table with a column for each term (resembling to entity) Also a extrinsic strategy will be added to the mix

design:

• sequence chart for indexing metadata
• table design to add to database

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Migrated from T715 (view on Phabricator)