[Admin] Add Prettier config

[tvdeyen]

Summary

Add a prettier config and adjust all admin JS files to the syntax rules.

Checklist

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• I have written a thorough PR description.
• I have kept my commits small and atomic.
• I have used clear, explanatory commit messages.

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[kennyadsl]

Thanks @tvdeyen!

Unrelated: do we need the chore(admin): part in the commit message? I don't think we ever used this format before, and we have the changelog tag already indicating where the change has effect. Despite I don't particularly like this format, I don't have strong preferences and I'm ok with you committing this way if you prefer. ❤️

[tvdeyen]

I don't mind changing it, but auto merge was already enabled.