Move seeding tests functionality into test module

[soapy1]

partially addresses #914

Description

This PR moves a module that is used to seed the db for testing from inside the app module to the testing module. This also allows for the removal of the tests that test this seeding

Pull request checklist

• Did you test this change locally?
• Did you update the documentation (if required)?
• Did you add/update relevant tests for this change (if required)?

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[soapy1]

This seemed like a little bit of a strange pattern to me. I'm not sure if this is a common pattern in python apps, happy to close this PR if it is. Otherwise, cleaning it up while working through speeding up tests.

[peytondmurray]

I certainly prefer this organization; these functions are exclusively used for building fixtures, which belong in conftest.py. I'm happy to merge this.