Currently when `timeseries_agg_helpers` is trying to create a time-series collection, it is actually just creating a normal (non-time-series) collection. This means that the jstests that are using the helper methods aren't actually testing time-series functionality.

In addition to fixing this bug, we should also make the documents created by this helper align more closely with the documents that tsbs creates. This will not only better mirror user workloads, but also allow us to test time-series behavior in more complex scenarios (ex. the time-series nested meta field behavior).