#### Summary of Changes
To avoid mixing the use of different shred storage types, each shred storage type
will have its blockstore in a different directory.
This PR still keeps the RocksFifo setting hidden. The default ShredStorageType and
blockstore directory are still RocksLevel and `rocksdb`.
Will follow-up with PRs on making FIFO option public in ledger-tool and validator.
#### Test Plan
* Added a new test to verify the existence of `rocksdb-fifo` directory when FIFO compaction is used.
* Updated existing test to verify the current setting still store ledger under `rocksdb` directory.
* Manually ran ledger_cleanup_test with both level and fifo compaction and verified the resulting ledger.
* Ran a validator with this PR.
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