Per-task allowed languages

[CristianCantoro]

Is your feature request related to a problem?
I would like the possibility to limit allowed languages (a subset of the languages allowed at contest level) per task.

We use CMS to assign a set of problems (tasks) to students and for most of them we are happy with solutions written either using C and C++, and C++ is recommended. However. for some tasks (approximation problems), that require a custom grader, we have only developed a C++ grader, thus we would like to be able to restrict the allowed languages for that task to just C++.

Describe the solution you'd like

At the moment, in the Contest configuration page, you can specify which languages are allowed.

I would like to have a similar checkbox, and an option in the task configuration files, to specify a subset of the allowed languages that can be used for a specific task.

Describe alternatives you've considered
An alternative would limit the allowed language to C+++ for the whole contest, but we would like to avoid that.

Additional context
Add any other context or screenshots about the feature request here.

Screenshot of the checkboxes marking the allowed languages in the Contest configuration page:

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