Add ignore_component_digest_mismatch option to db::config (default false).
When set, sstable loading logs a warning instead of throwing on component
digest mismatches, allowing a node to start up despite corrupted non-vital
components or bugs in digest calculation.
Propagate the config to all production sstable load paths:
- distributed_loader (node startup, upload dir processing)
- storage_service (tablet storage cloning)
- sstables_loader (load-and-stream, download tasks, attach)
- stream_blob (tablet streaming)
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