Studio: store only user overrides when uploading configs to firebase #451

Use Case

since we reduced most of the config files some time ago, we'd like to further simplify how config files are uploaded to firebase, for them to be fetched in cellpack studio. We want to store only the override values rather than the full set of defaults.

note: in Studio, when users download outputs including the config file, the full config is retrieved s3 which contains the complete config, so it is safe to store just the overrides in firebase.

Proposed Solution

• upload: upload only overrides in firebase, when a specified config file is attached to a pack job
• download: merge defaults after reading a firebase config file
• config should be optional on both ends, if no overrides provided, fall back to defaults
• upload client data without a specified config file shouldn't cause any hiccups