Tracking issue for Scale Process (with API v2)

## Development Task
The current HTTP API doesn't follow the RESTful API conventions. We have summarized some problems of the current status:
- mixed-use of `_` and `-`
- some methods are not accurate, e.g., we do not distinguish `PUT` and `POST`
- the resource should use a noun
- query parameter should not occur in the path
- mixed-use of singular and plural nouns

In addition, we can use `gin` as our HTTP web framework which is more popular and has a better ecosystem.