Automatically retry on Hyrax::LockManager::UnableToAcquireLockError

[maxkadel]

When we try to add a lot of FileSets at once, we are going to run into a lot of Hyrax::LockManager::UnableToAcquireLockError - this just means that the parent work has been locked and that FileSet hasn't been added to the parent successfully yet.

Acceptance criteria

• When importing a work with a lot of FileSets (e.g. 15 or more), if we hit a Hyrax::LockManager::UnableToAcquireLockError when trying to add the FileSet to the work, we should automatically retry that background job
• The retries should be on a backoff with increasingly longer times between retries until we hit a maximum number of tries
• After that maximum number of tries it should display in the UI