Use scripting to load data from CSV

Though yet to be tested, this may be effective in speeding up the time to insert a bulk of backlog data directly into the underlying graph data store in link-serv. In the Neo4j custom clustering implementation, one key detail to handle will be computing the cluster-wide `xid`.

This feature would be implemented completely outside the link-serv API service.

In the Encyclopedia of Life project, loading from CSV into Neo4j was seen to significantly speed up the insertion.

Neo4j:

https://neo4j.com/docs/cypher-manual/current/clauses/load-csv/

ArangoDB:

https://www.arangodb.com/docs/stable/programs-arangoimport-examples-csv.html

Start by reviewing the Neo4j custom clustering implementation and the linked Neo4j LOAD CSV and ArangoDB arangoimport documentation; no repository files or tests are named. Clarify how the standalone loader should compute the cluster-wide `xid` and how success will be measured before implementing it.

Written by the indexing model from the issue text.