Add origin_metadata_get API endpoint

I am adding an API end point to get origin intrinsic metadata to from origin_type and origin_url from indexer_storage. This involves adding an endpoint in origin.py and function that queries the db in service.py.

I use storage.origin_get to get basic origin information from the type and url. I use this to pass the id of the origin, to origin_metadata_get in indexer storage which returns to intrinsic metadata of the origin.

referencing #1613 (closed)

Migrated from D1623 (view on Phabricator)