Add prerequisites for practice exercises

[TomPradat]

This is the last batch about #983

Could i have an hacktoberfest-accepted label please ? 🙏

[github-actions]

Dear TomPradat

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[TomPradat]

Here is my solution : https://exercism.org/tracks/javascript/exercises/perfect-numbers/solutions/TomPradat

[TomPradat]

Here is my solution : https://exercism.org/tracks/javascript/exercises/luhn/solutions/TomPradat

I haven't added "array-analysis" despite the fact that I personally use Array#some as it does not seem necessary (as we can see in other community solutions)

[TomPradat]

Here is my solution : https://exercism.org/tracks/javascript/exercises/grains/solutions/TomPradat

I'm not sure about errors, I added it because you need to throw errors in the exercise. Though that's the case of many practice exercises, and the errors concept is very advanced in the hierarchy, what do you think ?

[SleeplessByte]

It's the right choice because you must understand how errors work. We can re-evaluate later.

[TomPradat]

Here is my solution : https://exercism.org/tracks/javascript/exercises/pythagorean-triplet/solutions/TomPradat

By the way I see a lot of exercises like this one using classes which is a pretty high level concept in the JS track. Should we reevaluate the use of classes in this exercise ? Not add the classes as a prerequisites ? Leave it as is ?

[SleeplessByte]

It's a good question. I think it's fine for now, we'll reevaluate together after if you want.

[TomPradat]

Here is my solution : https://exercism.org/tracks/javascript/exercises/palindrome-products/solutions/TomPradat

[SleeplessByte]

Looks good.