Keep receipts during GC

[LesnyRumcajs]

Summary

Right now, during GC run, we nuke receipts which are computationally expensive to regenerate. We should keep them. Consider adding environmental variable for this - by default let's keep the receipts.

Completion Criteria

• GC runs don't obliterate receipts - they are stored in the snapshot
• (optional) allow obliterating regardless, which could reduce disk space usage for use cases where receipts are not needed.

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