KG: export the edge tables (65% of nodes isolated) #421

Part of #386. Found by the quality pass (#420).

Right now 65% of the nodes are isolated. The exporter writes only four kinds of link, even though anon can read the source rows for most of the rest.

Emit the following links from the tables below:

• held_by from grant_investigators → investigators_public (resolves for 111 of 111)
• members from investigator_organizations (95)
• orcid and member_of_group from investigators_public (113 and 149)
• repo_url from software_tools, and expiration_date/open_date from funding_opportunities
• part_of_org from projects.organization_id, produced from project_publications, and funded_datasets from grant_dandisets/dandisets.award_numbers

Done when: the empty competency questions CQ03–CQ08, CQ12, CQ13, CQ16 and CQ17 answer (or are traced to missing data). Shapes #6, #14, #16 and #17 also need data to check.