Add extra fields to utxo events

[SupernaviX]

Add some fields to the wit definition of a "utxo" or "utxoundo" event:

• block-hash is the hash of the utxo's block
• block-height is the height of the utxo's block
• tx-hash: is the hash of the tx which contains the output
• index is the index of the output

As far as I can tell, other utxo-based chains would also have all of these fields associated with their utxos. So I think these all make sense to go in the wit, and don't need to be smuggled inside the utxo cbor (which is otherwise just straight-up utxorpc bytes)

[scarmuega]

can we match the approach used in the ledger interface above?

something like:

utxo {
  body: cbor,
  tx: txo-ref,
  block: block-ref
}

[SupernaviX]

updated