Include datums in query responses

Currently, ogmios only returns the datum hash from chain queries (e.g. server/src/Ogmios/Data/Json/Alonzo.hs):

encodeTxOut
    :: Crypto crypto
    => Al.TxOut (AlonzoEra crypto)
    -> Json
encodeTxOut (Al.TxOut addr value datum) = encodeObject
    [ ( "address"
      , Shelley.encodeAddress addr
      )
    , ( "value"
      , Mary.encodeValue value
      )
    , ( "datum"
      , encodeStrictMaybe encodeDataHash datum
      )
    ]

Our purposes require returning the datum value as well. This should be theoretically possible, as the chain index is capable of doing so.

[x] Investigate how the chain index attaches the datum to query responses According to @aske:

... plutus-chain-index writes datum values to the local sqlite db during chain sync which happens via the local chain sync ouroboros mini-protocol. Chain index uses ouroboros-network which seems to be able to return blocks with datum values included. Chain-index's endpoint "get datum by hash" returns a JSON repr of Datum from Ledger.
[ ] Find out if this functionality is supported by the Ouroboros mini-protocols
[ ] Implement inclusion of datum values in query responses

mlabs-haskell / ogmios

Include datums in query responses #4