Add Peru postal code validation

[RT1811]

Adds support for Peruvian postal codes to isPostalCode.

Changes:

• Added PE postal code validation
• Added valid and invalid Peru test cases
• Added PE to the supported locales in the README

Closes #2757

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (cdb7daf) to head (687e0a3).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2850   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          114       114           
  Lines         2599      2599           
  Branches       658       658           
=========================================
  Hits          2599      2599           

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