MM-38164: Paginate the GetPostThread API (#19485)

We implement a cursor based pagination model
to page through the posts in a given thread.

The cursor is a combination of the post.CreateAt+
post.Id to differentiate multiple posts in a given
timestamp.

Some additional parameters like direction, fromPost,
fromCreateAt and perPage were introduced to implement
this.

```release-note
NONE
```

store/timerlayer/timerlayer.go

@@ -4890,10 +4890,10 @@ func (s *TimerLayerPostStore) DeleteOrphanedRows(limit int) (int64, error) {
 	return result, err
 }
 
-func (s *TimerLayerPostStore) Get(ctx context.Context, id string, skipFetchThreads bool, collapsedThreads bool, collapsedThreadsExtended bool, userID string) (*model.PostList, error) {
+func (s *TimerLayerPostStore) Get(ctx context.Context, id string, opts model.GetPostsOptions, userID string) (*model.PostList, error) {
 	start := timemodule.Now()
 
-	result, err := s.PostStore.Get(ctx, id, skipFetchThreads, collapsedThreads, collapsedThreadsExtended, userID)
+	result, err := s.PostStore.Get(ctx, id, opts, userID)
 
 	elapsed := float64(timemodule.Since(start)) / float64(timemodule.Second)
 	if s.Root.Metrics != nil {