Move away from manually updating tests/integration-tests.txt #12822

Right now we manually update tests/integration-tests.txt when we add new API tests. We do this simply because I was in a hurry when I first implemented this and couldn't quickly figure out a better way to do it.

We document it here: https://guides.dataverse.org/en/6.12.1/developers/testing.html#writing-api-tests-with-rest-assured

"If you are adding a new test class, be sure to add it to tests/integration-tests.txt so that our automated testing knows about it."

So when we come up with a fix, we should delete or update the line above.