Export api::v2::updates enums as part of unofficial unstable API

Up until commit 9f937dd ("Switch to using new stream authentication
request message format") we were exporting the api::v2::updates::Request
enum, which formed part of our undocumented, unofficial, and unstable
API.
With said change, however, we missed to export the resulting two newly
introduced enum types. Do it now.

CHANGELOG.md

@@ -1,3 +1,9 @@
+Unreleased
+----------
+- Exported `api::v2::updates::{Authenticate,Listen}` enums as part of
+  unofficial unstable API
+
+
 0.27.0
 ------
 - Added support for overwriting default realtime data bar, quote, and

src/api/v2/updates.rs

@@ -168,8 +168,10 @@ pub struct Authentication {
 /// A control message authentication request sent over a websocket
 /// channel.
 #[derive(Debug, Deserialize, Serialize)]
+// Part of unofficial unstable API.
+#[doc(hidden)]
 #[serde(tag = "action")]
-enum Authenticate<'d> {
+pub enum Authenticate<'d> {
   /// A request to authenticate with the server after a websocket
   /// connection was established.
   #[serde(rename = "auth")]
@@ -184,8 +186,10 @@ enum Authenticate<'d> {
 
 /// A control message listen request sent over a websocket channel.
 #[derive(Debug, Deserialize, Serialize)]
+// Part of unofficial unstable API.
+#[doc(hidden)]
 #[serde(tag = "action", content = "data")]
-enum Listen<'d> {
+pub enum Listen<'d> {
   /// A request to listen to a particular stream.
   #[serde(rename = "listen")]
   Request(Streams<'d>),