DeleteTripsSnapshotSpec:
+ https://iceberg.apache.org/docs/1.5.1/spark-procedures/#snapshot 
A snapshot
- should blow up if the underlying data is deleted !!! IGNORED !!!
- should create no new files for copy-on-write !!! IGNORED !!!
- should insert creates new files for copy-on-write !!! IGNORED !!!
- should be cleaned up with remove_orphan_files !!! IGNORED !!!