Add RPC route to get note witness

[danield9tqh]

Summary

Adding RPC route to get the witness for a specific note index.

Testing Plan

Unit test and local testing

Documentation

Does this change require any updates to the Iron Fish Docs (ex. the RPC API
Reference)? If yes, link a
related documentation pull request for the website.

Documentation: iron-fish/website#342

[X] Yes

Breaking Change

Is this a breaking change? If yes, add notes below on why this is breaking and
what additional work is required, if any.

[ ] Yes

[hairtail]

This is really helpful. With this pr, we can create transaction and sign a transaction locally i guess. There is one more route chain/postTransaction needed i think. I would like to provide service with all chain/xxx routes but i will disable rpc call for to wallet/xxx for my node.

[NullSoldier]

nice can you also add the documentation for this too?

[danield9tqh]

@hairtail the wallet/postTransaction also marks the notes in that transaction as spent. Where would you keep track of unspent notes if not in the wallet? Are you doing that outside the node currently?

[hairtail]

@hairtail the wallet/postTransaction also marks the notes in that transaction as spent. Where would you keep track of unspent notes if not in the wallet? Are you doing that outside the node currently?

I want to send transaction with a known note which called causal send. That to say,

1. I receive some token in transaction A.
2. I want to send the received token in transaction A to address X in transaction B locally with these rpc calls without wallet import.
3. The consensus is responsible for the validation of transaction B.

[danield9tqh]

@hairtail We do have some of that functionality but it is a little confusing currently. The one thing we don't have is an endpoint to create + sign a raw transaction from a list of notes + outputs which I think is what you're asking for. I think @hughy is going to pick this up in the coming weeks.

We also have a endpoint that you can broadcast a signed transaction. That's in wallet/addTransaction