Use causal consistency in change_streams_secondary_reads passthrough

The test suite mostly gets away with not using causal consistency because most assertions are along the lines of

assert.soon(() => changeStream.hasNext());

which are pretty tolerant of visibility rules. However, we've seen a couple failures in this suite that would be addressed by using causal consistency, and it would make the suite more robust in the future, making it easier to add new tests to the jstests/change_streams directory.