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
```

app/file.go

@@ -367,7 +367,7 @@ func (a *App) MigrateFilenamesToFileInfos(post *model.Post) []*model.FileInfo {
 	fileMigrationLock.Lock()
 	defer fileMigrationLock.Unlock()
 
-	result, nErr := a.Srv().Store.Post().Get(context.Background(), post.Id, false, false, false, "")
+	result, nErr := a.Srv().Store.Post().Get(context.Background(), post.Id, model.GetPostsOptions{}, "")
 	if nErr != nil {
 		mlog.Error("Unable to get post when migrating post to use FileInfos", mlog.Err(nErr), mlog.String("post_id", post.Id))
 		return []*model.FileInfo{}