update kms credential todo (#760)

Author: abr-egn

src/client/csfle/state_machine.rs

@@ -181,7 +181,10 @@ impl CryptExecutor {
                         })
                         .await?;
                 }
-                State::NeedKmsCredentials => todo!("RUST-1314"),
+                State::NeedKmsCredentials => {
+                    // TODO(RUST-1314, RUST-1417): support fetching KMS credentials.
+                    return Err(Error::internal("KMS credentials are not yet supported"));
+                },
                 State::Ready => {
                     let (tx, rx) = oneshot::channel();
                     let mut thread_ctx = std::mem::replace(