Allowlist Database/MultipleDatabases offenses

- config/initializers/sidekiq.rb this method is safe for multiple
  databases
- lib/gitlab/database.rb is a legitmate use
- lib/gitlab/database/load_balancing/load_balancer.rb uses methods that
  are safe with multiple databases
- lib/gitlab/database/migrations/observers/query_log.rb also uses a
  method that is safe with multiple databases
- lib/tasks/gitlab/db/validate_config.rake is OK because it's executed
  in the context of looping through each database.