Utilize Incremental PDT for sessions

[IchordeDionysos]

With Looker 21.4 there is now support for (experimental) support for Increment persistent derived table (PDT).

https://docs.looker.com/data-modeling/learning-lookml/incremental-pdts

I think that using this with sessions could make analyzing sessions more efficient as the session start and end don't have to be recalculated for 3-year-old sessions.