feat(seer grouping): Add call to Seer to optimized grouping flow in ingest

[lobsterkatie]

There are currently two paths ingest can follow when saving an event: the existing _save_aggregate (which runs unnecessary calculations when a project is in a grouping config transition) and the newer _save_aggregate_new (which only does extra calculations when necessary). Until now, Seer grouping had only been integrated into the first path, meaning we had to turn off the second path entirely. This adds the Seer logic to the new path, so we don't have to choose between the features.

Note: The tests look like they've changed more than they actually have. In reality, all that's happened is that the body of each test has been parameterized and wrapped in the following code, which forces it to run through both paths mentioned above:

for use_optimized_grouping, existing_event_message, new_event_message in [
    (True, "Dogs are great!", "Adopt don't shop"),
    (False, "Maisey is silly", "Charlie is goofy"),
]:
    with patch(
        "sentry.event_manager.project_uses_optimized_grouping",
        return_value=use_optimized_grouping,
    ):