MM-35206 CRT: is_following on posts not reflecting state properly (#17533)

* forgot to copy isFollowing param

* /thread API didn't return thread posts, just the root

* cleanup

* [ci]

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

model/post.go

@@ -207,6 +207,7 @@ func (o *Post) ShallowCopy(dst *Post) error {
 	dst.Participants = o.Participants
 	dst.LastReplyAt = o.LastReplyAt
 	dst.Metadata = o.Metadata
+	dst.IsFollowing = o.IsFollowing
 	dst.RemoteId = o.RemoteId
 	return nil
 }