Update backend to use malware scanning buckets for files

[joshgamache]

Describe the task

With the completion of #2663, file scanning is enabled in our file storage on GCP/GCS. Three buckets are now available -unscanned, -clean, -quarantined. The -unscanned bucket should be the target of initial uploads, but we'll need to find a way to determine when a file has finished scanning/confirmed clean. We can create a trigger (just like the one that exists for -unscanned) in GCP for when a file arrives in the -clean and -quarantined buckets, which could trigger a Cloud function to inform the backend to update the status/location/etc of the file. Alternatively, the backend could monitor the buckets itself, updating as needed.

Acceptance Criteria

• first
• second
• third

Definition of Done

• first
• second
• third

Additional context

• Add any other context about the task here.
• Or here

[zoeyli-46]

frontend ticket here! #558