[TEST] Migrate over to `github.com/ory/dockertest` v4

[gregfurman]

Context

The container testing library we use for our integration tests has been upgraded to v4. This introduces quite a few improvements along with some breaking changes.

See https://github.com/ory/dockertest/blob/v4/UPGRADE.md

Task

• Follow the migration guide for moving from v3 to v4.
• Manually verify some integration tests that use this library are passing (don't need to run the entire suite).