BED-4194: PG Migrator Testing

[maffkipp]

Description

This PR adds integration tests for our migrator tool that handles importing nodes, edges, and kinds from neo4j into postgres. It also adds some minor refactors to the migrator itself to make it easier to test, and upgrades our integration testing postgres db from 13.2 to 16.1.

Motivation and Context

We are planning on using this migrator to assist in switching customers over to our postgres graph driver, but we want to make sure it has adequate test coverage first.

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Chore (a change that does not modify the application functionality)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• Documentation updates are needed, and have been made accordingly.
• I have added and/or updated tests to cover my changes.
• All new and existing tests passed.
• My changes include a database migration.

[zinic]

Looks like we got dinged with a merge conflict but otherwise so far so good. One minor nit for the in-progress work.