[Backend] Edit Task

[fmcubium]

See Issue #87.

Create an API endpoint that accepts updated information about a task and updates the relevant object in the Task DB table.

Anyone tackling this issue must mark the TestTaskEditing class as required on test.py if it is not already marked as so and ensure that said tests pass.

[Jaefae]

I'd like to work on this. I'll add a TestTaskEditing class to tests.py following the same pattern as the other tests (auth/ownership checks, invalid input, nonexistent task, etc.). Once those look good I can also work on the edit_task endpoint implementation.

[fmcubium]

Implementation of tests isn't necessary for this, just make sure to mark the category as required