feat(isPostalCode): Add PK (Pakistan) locale

[mateeni-dev]

Added validation and tests for postal code locale PK

Reference for valid list of postal codes: https://www.pakpost.gov.pk/postcodes.php

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (86a07ba) to head (a56b4d5).
Report is 155 commits behind head on master.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files          104       104           
  Lines         2203      2203           
  Branches       477       477           
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  Hits          2203      2203           

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[pano9000]

thank you for this addition.
it looks good to me, only thing I personally don't like is the link to the URL being inside the isPostalCode.js

generally speaking: thank you for providing some official reference for the numbers, and I agree that there should be some place, where all of that information is stored/made available, but I'm not sure if isPostalCode.js would be the best place for that - it would get really messy in that file, otherwise, if every language had 1 or maybe even 2 references in there.

[WikiRik]

Please fix the merge conflicts

[mateeni-dev]

Please fix the merge conflicts

done