🐛 Fixed commenting on tier-only posts (#15333)

fixes https://github.com/TryGhost/Team/issues/1860

**Problem:**
Members were not able to comment on a post that was only visible for members with a specific tier.

**Causes:**
Content gating was done on models with missing relations.
- The products relation was not loaded on the member when doing content gating
- The tiers relation was not loaded on the post when doing content gating

**Tests:**
- Added for tier-only posts
- Added for paid-only commenting

ghost/core/core/server/services/comments/service.js

@@ -160,7 +160,8 @@ class CommentsService {
             id: member
         }, {
             require: true,
-            ...options
+            ...options,
+            withRelated: ['products']
         });
 
         this.checkCommentAccess(memberModel);
@@ -169,7 +170,8 @@ class CommentsService {
             id: post
         }, {
             require: true,
-            ...options
+            ...options,
+            withRelated: ['tiers']
         });
 
         this.checkPostAccess(postModel, memberModel);
@@ -208,7 +210,8 @@ class CommentsService {
             id: member
         }, {
             require: true,
-            ...options
+            ...options,
+            withRelated: ['products']
         });
 
         this.checkCommentAccess(memberModel);
@@ -229,7 +232,8 @@ class CommentsService {
             id: parentComment.get('post_id')
         }, {
             require: true,
-            ...options
+            ...options,
+            withRelated: ['tiers']
         });
 
         this.checkPostAccess(postModel, memberModel);