We would like to store backup logs either in dynamodb, or if their size is too big, store them in blob service. Report service already implements a similar functionality so this diff moves the struct to comm-lib. Some small changes were made:
- Added a new() function so there's less chance that people will create the in-blob variant manually
- Renaming and added some more comments
- Now during (de-)serialization to dynamodb values the caller must pass the attribute names