Set retries of of import Stage workers and AdvanceStage workers to 6
### About We tend to set the Sidekiq retries of our `Stage` and `AdvanceStageWorker`s to `3` (although this is consistent, Github Stage workers get 5). These workers can run for a long time, so can be more prone to things like service interruptions. We'd like them to be more resilient. ### Proposal Set the retries to `6` for Stage and AdvanceStage workers. 6 will make them more resilient to system interruptions. The exponential retry backoff will mean 6 retries will introduce nearly [20m total wait time](https://github.com/sidekiq/sidekiq/wiki/Error-Handling#automatic-job-retry). Any higher retry will hold up an import for too long.
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