Add dry_run parameter to Search::IndexCurator

What does this MR do and why?

As we roll out search index curation across GitLab's elasticsearch indices, we need the ability to do dry runs. This will allow us to monitor the logs and ensure everything is working properly before enabling.

These are related MR's to this process:

• Add dry run capability: !103959 (merged) 👈
• Add inclusion parameter to support excluding everything besides specified indices: !103951 (merged)
• Add feature flags to toggle which indices should be added to inclusion parameter: !104423 (merged)
• Add an ops feature flag that toggles dry_runparameter in Search::IndexCurationWorker: !104321 (merged)

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