feat: Include dart challenges

[shan-shaji]

Is your feature request related to a problem? Please describe.
Since the app currently only supports python and javascript. It would be better if the app contains tutorials for multiple languages.

Describe the solution you'd like
I would like to add tasks for dart language

Describe alternatives you've considered
N/A

Additional context
N/A

[welcome]

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[shan-shaji]

Hey, @jamesgeorge007 can you please assign this to me? I am working on this.