- Add CopyColumnUsingBackgroundMigrationJob background
  migration to update the value of a column using
  the value of another column in the same table
  It provides support for tracking the jobs through the
  use of Gitlab::Database::BackgroundMigrationJob,
  runs updates in sub batches, can run against tables
  with a column that is not named id and can be used with
  queue_background_migration_jobs_by_range_at_intervals
- Add initialize_conversion_of_integer_to_bigint
  migration helper to start the first phase of the conversion
  of an integer column to bigint