Add the table to track user acknowledgments.

Table structure was described in ENG-1868.

There is a code duplication between this and https://phab.comm.dev/D5307 - looks like the idea of setup-db was to create an entire database with one query, but if it can be done differently I will extract this query to one function and run the same code in both migration and here.

1. Create locally new database (to avoid overriding local database with mock data) and gave permissions to comm@localhost
2. Update db_config.json with new database name
3. Run keyserver and check if database was created with policy_acknowledgments table.