lnrpc/signrpc+lnwallet/rpcwallet: expose local nonces over RPC

In this commit, we update the set of protos to accept the local secret
nonces over RPC. This is actually a 97 byte value, as it includes the
two 32 byte nonces, as well as the 33 byte value of the public key of
the signer.

This is needed in order to be able to open taproot channels over the RPC
interface.

docs/release-notes/release-notes-0.17.0.md

@@ -244,6 +244,13 @@ None
 * Add [`--unused`](https://github.com/lightningnetwork/lnd/pull/6387) to
   `lncli newaddr` command.
 
+* [The `MuSig2SessionRequest` proto message now contains a field to allow a
+  caller to specify a custom signing
+  nonce](https://github.com/lightningnetwork/lnd/pull/7994). This can be useful
+  for protocol where an external nonces must be pre-generated before the full
+  session can be completed.
+
+
 ## Code Health
 * Updated [our fork for serializing protobuf as JSON to be based on the
   latest version of `google.golang.org/protobuf` instead of the deprecated