Finalize RemoveDuplicatesLfsObjectsProjects background migration

Context

After #199909 (closed) is completed, we need to validate that the batch background migration is completed.

For this issue, we should create a migration with ensure_batched_migration_is_finished according to https://docs.gitlab.com/ee/development/database/batched_background_migrations.html#finalize-a-batched-background-migration and prepare the async index in a post migration with DEPENDENT_BATCHED_BACKGROUND_MIGRATIONS that adds the unique index for lfs_objects_table by project_id and repository_type.

Considerations

According to our docs:

We recommend that batched background migrations are finalized after all of the following conditions are met:

• The batched background migration is completed on GitLab.com
• The batched background migration was added in or before the last required stop