vendor-fetch clears all the comments in the project.json file.

## Issue The `c3c vendor-fetch` command clears all the comments in the project.json file. Maybe the user have put something on his own to document something or to make sense of something in the future or to explain why a line was put there. But doing `c3c vendor-fetch` just clears all the comments. ## Expected Behaviour The comments should stay the same. The comments on seperate lines and the comments on the same line as a key should stay exactly the same. If any key is to be added to the project.json file, it should go to the end of the file without changing any line already existing in the file. ### Note This issue is the continuation of #3233