Add GetPostsForChannel method to plugin API (#9557)

Signed-off-by: Akash Srivastava <akash.srivastava@openebs.io>

plugin/api.go

@@ -173,6 +173,9 @@ type API interface {
 	// GetPost gets a post.
 	GetPost(postId string) (*model.Post, *model.AppError)
 
+	// GetPostsForChannel gets a list of posts for a channel.
+	GetPostsForChannel(channelId string, page, perPage int) (*model.PostList, *model.AppError)
+
 	// UpdatePost updates a post.
 	UpdatePost(post *model.Post) (*model.Post, *model.AppError)