Fix error "Cannot transition status via :start from :started" in BulkImports::PipelineBatchWorker

When BulkImports::PipelineBatchWorker is retried due to a network error when downloading the exported relation files, the worker tries to change the status of BulkImports::BatchTracker from started to started, which causes the error: Cannot transition status via :start from :started (Reason(s): Status cannot transition via "start"). This error occurs because such a status transition is not allowed. Therefore, we should allow such transition or update the worker not to change the status to started if the status is already started.

Proposed solution

Allow the start event in BulkImports::BatchTracker to transit from started to started similar is done in BulkImports::Tracker.

Note

Allowing such a transition can cause duplicated records in case the worker is retried due to a Sidekiq restart and the pipeline has already started to import records. Having said that, this is less likely to occur on batched migrations since a small dataset is used so most of the time the worker will finish during the Sidekiq restart graceful period

The duplicated record issue will be fixed in #424954 (closed)