Config: Preset ALWAYS overrides Ledger

[sgillespie]

Currently, if using a preset, you cannot also configure the ledger. This is because the preset overrides ALL other options. This means that, in following config,

"insert_options": {
  "preset": "only_utxo",
  "ledger": "enable"
}

The ledger setting will have no effect. We would like to allow users to specify the ledger setting along with the prefix, and set a default if none is specified ("enable").

One way to do this would be to add a Ledger field to all of the preset constructors: https://github.com/IntersectMBO/cardano-db-sync/blob/master/cardano-db-sync/src/Cardano/DbSync/Config/Types.hs#L149