cli: add multiwallet capability to GetNewAddress and -generate

Summary:
This is a backport of [[bitcoin/bitcoin#19133 | core#19133]] [8/10]
bitcoin/bitcoin@4b859cf

Depends on D9947

Test Plan: `ninja all check-all`

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9948

src/bitcoin-cli.cpp

@@ -959,9 +959,14 @@ static void GetWalletBalances(UniValue &result) {
  * @returns getnewaddress response as a UniValue object.
  */
 static UniValue GetNewAddress() {
+    std::optional<std::string> wallet_name{};
+    if (gArgs.IsArgSet("-rpcwallet")) {
+        wallet_name = gArgs.GetArg("-rpcwallet", "");
+    }
     std::unique_ptr<BaseRequestHandler> rh{
         std::make_unique<DefaultRequestHandler>()};
-    return ConnectAndCallRPC(rh.get(), "getnewaddress", /* args=*/{});
+    return ConnectAndCallRPC(rh.get(), "getnewaddress", /* args=*/{},
+                             wallet_name);
 }
 
 /**