[backup] Update dynamodb

Summary:
ENG-4497

Two changes:

• we remove recoveryData from backup items because backup_id can be merged with it more context here
• add userKeys to projected attributes because it will need to be available to fetch as "latest backup"
  • also possible: do two fetches to the db, one for backup_id and second one (from the main table) for the user_keys

Depends on D8953

Test Plan: yarn reset-local-stack, tested with future diffs

Reviewers: bartek, patryk, kamil, jon

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8954