refactor arknote as fake vtxo

[louisinger]

This PR is refactoring arknote. It also drops the "note" DB Table and repository.
breaking change.

Fake VTXO note

A note now looks like the following :

arknoteSkB92YpWm4Q2ijQHH34cqbKkCZWszsiQgHVjtNeFF2Cwp59D

the string embed a 32 byte preimage & the value of the note (4 BE bytes).

When creating a note via AdminService.CreateNotes, the server adds a domain.Vtxo to the database. This VTXO has an empty roundTxId field and is locked by a taproot pkscript with a unique tapscript:

SHA256
<preimageHash>
OP_EQUAL

The fake vtxo is identified by the preimageHash:0 outpoint.

Thus, a note can be registered as input of the BIP322 intent transaction.

API changes

• remove notes from RegisterIntent RPC
• remove notes from RegisterInputsForNextRound RPC
• update TxRequestInfo message
• the only way to redeem a note is to include it in Bip322Signature field.

@Kukks @altafan please review