Apply differential privacy on watchlist report

Changes:
- Added watchlist report generation functions
- Apply DP to watchlist report
- Renamed WatchlistSettings as WatchlistConfig
- WatchlistSettings now stores user generated settings

Bug: 63908748
Test: Able to compile, tests pass

Change-Id: I5a4e3f7e5e1195203aa0a66fa4b9e7ed4e0c1b27