Refining the threshold for total_umis

[brianraymor]

Per @ambrosejcarr in his review of Add UMI count filter to optimus ETL
It would be appropriate to make a backlog issue to record the existence of open questions:

1. if there is a common user preference for a specific value for the total_umis threshold, and if not,
2. whether users should be enabled to adjust the threshold parameter in the matrix service API.

August 6 - Guidance from AWG

Short-term goal

• Emptydrops or CellRanger cut-off? (Need to use a new version of emptydrops.)
• Give the option to get the full matrix but not as a default.