snapshot-converter: HACK read salt from bloomfilter files

[jasagredo]

While we wait for IntersectMBO/lsm-tree#855 we are going to read the salt from one of the exported files.

[geo2a]

Approving, provided that you've tested that the conversion works downstream (I saw that you asked JP for a snaphot to try this hack on).

[jasagredo]

Tested locally with a snapshot @jpraynaud provided:

❯ # InMemory to LSM
❯ cabal run -v0 exe:snapshot-converter --  convert --snapshot-in ~/Downloads/116074908 --snapshot-out ./116074908 --lsm-export-to ./116074908_exported --config ../cardano-node/configuration/cardano/mainnet-config.json
Reading ledger state from 116074908... Done
Copying state file...Done
Streaming ledger tables...Done
Generating new metadata file...Done
❯ # LSM import
❯ cabal run -v0 exe:snapshot-converter -- lsm import --lsm-database lsm --lsm-import-from 116074908_exported --snapshot 116074908
Done
❯ # LSM export
❯ cabal run -v0 exe:snapshot-converter -- lsm export --lsm-database lsm --lsm-export-to 116074908_exported_2 --snapshot 116074908
Done
❯ # LSM to InMemory
❯ cabal run -v0 snapshot-converter --  convert --snapshot-in ./116074908 --lsm-import-from ./116074908_exported_2 --snapshot-out ./116074908_mem --config ../cardano-node/configuration/cardano/mainnet-config.json
Reading ledger state from 116074908... Done
Copying state file...Done
Streaming ledger tables...Done
Generating new metadata file...Done
❯ # Diff InMemory snapshots
❯ diff 116074908_mem/tables ~/Downloads/116074908/tables && diff 116074908_mem/meta ~/Downloads/116074908/meta && diff 116074908_mem/state ~/Downloads/116074908/state
❯ echo $?
0