Add RocksSlotTtl storage type: A slot-based FIFO compatible with Level

[yhchiang-sol]

Summary of Changes

This PR introduces ShredStorageType::RocksSlotTtl. The shred storage type
that works similarly to FIFO except it uses a slot-based TTL to purge files and
it's compatible with level compaction.

Under the hood, RocksSlotTtl has no background compaction, and it relies on
the recently introduced #26651 that enables LedgerCleanupService to directly
purge any sst files that are older than both --limit-ledger-size and root.

I am still baking the PR and will soon start running experiments. If the experimental
results sound, then RocksSlotTtl should have similar performance as FIFO but
have a stronger consistency guarantee than FIFO and is compatible with the existing
level compaction.

[yhchiang-sol]

Crap. This doesn't work because DeleteFilesInRange does not cover L0. Such a pity :'(.