Add option to index UTxOs by stake address

[whankinsiv]

At present, utxo_state only keys UTxOs by (tx_hash, output_index), which requires lookups by stake-address to scan the entire UTxO.

Add a config option store-accounts to utxo_state that maintains a Vec<UTXOKey> mapped to each StakeCredential. This will enable the implementation of the /accounts/{stake_address}/utxos REST handler and is one of the three ways Blockfrost exposes UTxO balances.

[whankinsiv]

To avoid doubling our on disk storage of UTxOs, I will be implementing this ticket by indexing ShelleyAddresses by StakeAddress in historical_accounts_state and lookups of UTxOs will be served from address_state.

Query stake account payment addresses -> Query each payment address for UTxOs -> Construct REST response