Replace Discussion stubs with new recommend signature + types

The previous stub was unused. This adds relevant types and signatures for the
`recommend` method.

This PR is based off commits in #111. This change adds `recommend` by
itself so that it can be implemented soon by Android and iOS.

We can release the remaining Discussion methods in another Bridget
version, so the platforms can implement them when ready. This will
enable us to render more articles with discussion using DCAR, more
quickly.

Co-authored-by: Jamie B <[email protected]>
Co-authored-by: Ioanna Kokkini <[email protected]>
Co-authored-by: Charlotte <[email protected]>

.changeset/tasty-dolls-protect.md

@@ -0,0 +1,5 @@
+---
+"bridget": minor
+---
+
+Replace previous disucssion service stubs with new recommend signature

thrift/native.thrift

@@ -59,13 +59,6 @@ union Metric {
     3: MetricFont font;
 }
 
-struct CommentResponse {
-    1: required string status;
-    2: required i32 statusCode;
-    3: required string message;
-    4: optional string errorCode;
-}
-
 enum PurchaseScreenReason {
     hideAds = 0,
     epic = 1
@@ -137,12 +130,24 @@ service Metrics {
     void sendMetrics(1:list<Metric> metrics)
 }
 
+struct DiscussionApiResponse {
+    1: required string status;
+    2: required i32 statusCode;
+    3: required string message;
+    4: optional string errorCode;
+}
+
+enum DiscussionNativeError {
+    UNKNOWN_ERROR = 0
+}
+
+union DiscussionResponse {
+    1: DiscussionApiResponse response;
+    2: DiscussionNativeError error;
+}
+
 service Discussion {
-    string preview(1:string body),
-    bool isDiscussionEnabled(),
-    bool recommend(1:i32 commentId),
-    CommentResponse comment(1:string shortUrl, 2:string body),
-    CommentResponse reply(1:string shortUrl, 2:string body, 3:i32 parentCommentId)
+    DiscussionResponse recommend(1:string commentId),
 }
 
 service Analytics {