[Doc][Link] Links in the website are deprecated

## Documentation Scope
This repo's [github action](https://github.com/apache/incubator-devlake-website/actions/runs/5605449697/jobs/10254590212) fails every day, cause of deprecated links in the website's document.

## Describe the Change

After checking the errors, I found that link to code like `https://github.com/apache/incubator-devlake/blob/main/generator/template/plugin/tasks/task_data.go-template` should be `https://github.com/apache/incubator-devlake/blob/main/backend/generator/template/plugin/tasks/task_data.go-template`. (Just add a `/backend` in the file path.)

## Screenshots

## Additional context
Other 404 links are unexpected, we can fix the links to code details, and see what happends to this checker.