Include postal code example per country/subdivision

[Etroid]

Problem/Motivation

There are many scenarios in which the postal code validation return ambiguous error messages. It might be useful to provide some additional context through a valid example. Google provides a list of valid postal code examples under the zipex property. As a first step to improve postal code validation, we would need to include this property in the addressing resources.

Example

What's involved:

• Update generate_address_data.php to include zipex on both country and subdivision level
• Add property postalCodeExample to AddressFormat class
• ?

Related: #31

[jamessampford]

I think this would be a great addition as this will show an example as to what was expected by the validator

[bojanz]

I need to resolve #147 first because if we give up on subdivision-level postal code validation, then we don't need postal code examples on that level either.

[BenWalters]

@bojanz since #147 is now 'resolved' is there an appetite to implement the examples at country level?

[bojanz]

@BenWalters
Yes, let's circle back to this. I think we need a new PR though.

[damienmckenna]

Just ran into this with the following values from El Salvador:

• 1101
• CP1101

Both failed validation, but both are "shorthand" for the postal code, and in both cases it gave the vague "Postal code field is not in the right format." message.