Add an automatic pipeline for contributing new problems to the repository

[CIGbalance]

We want people to be able to add new problem descriptions to the repository easily, but at the same time ensure that the added content is compatible with the existing problems. The suggested worflow is as follows:

• Contributor adds a problem to a new file and makes a PR
• New file is automatically validated on GitHub, and an additional manual review is required
• Once the review is positive and checks pass, on merge (button-push on GitHub) the content of the new file is automatically added to the big json file