Automate the generation of unit test json returns

[patricklatimer]

The json return examples in src/aind_slims_api/tests/resources are manually fetched and copied in, which makes it useful for regression testing of our code but brittle to SLIMS database changes. We should have an easy way to regenerate those when there's an update to the SLIMS schema itself, so that we don't have code that passes unit tests but fails integration tests.