New oracle add_note api.

[LeilaWang]

We should let the contracts define what can be stored.

Sometimes the information of notes are shared offline. And the users should be able to either:

• Call a contract function with the preimage:

fn redeem_a_token(preimage, nonce) {
  let note = Note::new_with_nonce(preimage, nonce);
  set.assert_contains_and_remove(note);
  increase_balance();
}

• Or add the preimage to the oracle db:

unconstrained claim_a_token(preimage, nonce) {
  let note = Note::new_with_nonce(preimage, nonce);
  oracle.add_note(state_var.storage_slot, note);
}

Because the contract developers will know what data would be shared offline, it makes sense for them to provide the proper apis accordingly.

This should replace the previous proposal of adding addPreimage(contract_address, storage_slot, preimage) api to the AztecRPCServer. Which will require the users to provide the storage_slot. And might not be obvious what's been added.