PHPLIB-912: Fix changestream creation to avoid errors on sharded clusters

[alcaeus]

PHPLIB-912

This is one possible way to fix the issue of certain tests sporadically failing on sharded clusters. My initial attempt to only pass a startAtOperationTime still caused failures, as the operation time of the previous command (in this case the create command to create the test collection) occurred within the same second and was thus captured by the change stream. To reduce sleep time to a minimum (as this applies to every test involving a change stream), we only sleep long enough to have the timestamp tick over to the next second.

This is something we may want to call out in the spec. I don't know if other drivers are facing the same issues (I'd expect they are), but it might be helpful to record this somewhere in the unified test format specification.