Add num_rows estimate in hub_cache
Added estimated_num_rows to config-size, dataset-size, and I also updated `hub_cache` to use estimated_num_rows if possible as `num_rows` (this way no need to modify anything in moon)

TODO

- [x] mongodb migration of size jobs
- [x] update tests
- [x] support mix of partial and exact num_rows in config-size and dataset-size
- [x] revert sylvain's suggestion to add "num_rows_source" that is actually not needed
Add num_rows estimate in hub_cache: Added estimated_num_rows to config-size, dataset-size, and I also updated `hub_cache` to use estimated_num_rows if possible as `num_rows` (this way no need to modify anything in moon)

TODO

- [x] mongodb migration of size jobs
- [x] update tests
- [x] support mix of partial and exact num_rows in config-size and dataset-size
- [x] revert sylvain's suggestion to add "num_rows_source" that is actually not needed