feat: new concept exercise - appointment-time

[sahamdot]

Added new concept exercise, appointment-time.

Closes #1528.

[github-actions]

Dear SalahuddinAhammed

Thank you for contributing to the JavaScript track on Exercism! 💙
You will see some automated feedback below 🤖. It would be great if you can make sure your PR covers those points. This will save your reviewer some time and your change can be merged quicker.

• 📜 The following files usually contain very similar content.

  • concepts/<concept>/about.md
  • concepts/<concept>/introduction.md
  • exercises/concept/<exercise>/.docs/introduction.md

  Please check whether the changes you made to one of these also need to be applied to the others.

• 🧦 If you changed the function signature or the JSDoc comment in the exemplar file (.meta/exemplar.js) or the stub file (<exercise>.js), make sure the change is applied to both files.

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• 🔤 If your PR fixes an easy to identify typo, if would be great if you could check for that typo in the whole repo. For example, if you found Unicdoe, use "replace all" in your editor (or command line magic) to fix it consistently.

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• 📏 Make sure you set the appropriate x:size label for the PR. (This also works after merging, in case you forgot about it.)

• 🔍 Don't be too nit-picky. If the PR is a clear improvement compared to the status quo, it should be approved as clear signal this is good to be merged even if the minor comments you might have are not addressed by the contributor. Further improvement ideas can be captured in issues (if important enough) and implemented via additional PRs.

• 🤔 After reviewing the diff in the "Files changed" section, take a moment to think about whether there are changes missing from the diff. Does something need to be adjusted in other places so the code or content stays consistent?

_{Automated comment created by PR Commenter 🤖.}

[SleeplessByte]

Thank you for working on this in the past. I am sorry you never got to see this merged.
Lots of stuff happened since then.

Because you deleted your branch I cannot reopen this and get it merged, so I will recreate the content and keep you as author as I make changes to get this released.