Should place SDFormat files for integration tests in one location

[azeey]

Desired behavior

To have a standard location for SDFormat files used in integration testing.

Alternatives considered

n/a

Implementation suggestion

I propose we move all SDFormat files used for integration tests into test/sdf. Currently, some files are in test/sdf and others are in test/integration/. This causes confusion as to where to place new SDFormat files when writing tests.

Additional context

n/a