Valid DHL eCommerce tracking numbers fail validation

[dan-jensen]

Problem

This gem seems to support DHL eCommerce, but DHL eCommerce tracking numbers fail validation.

It seems the problem is this gem expects DHL eCommerce tracking numbers to start with a 2-letter prefix [like "GM"](https://github.com/jkeen/tracking_number_data/blob/d536725bede567e878a6b35639f8d6ddb86f22b0/couriers/dhl.json#L56, but in my experience they are all-numeric (14 digits).

These are real DHL eCommerce tracking numbers generated between May and July, 2024:

dhl_ecommerce_tracking_numbers = %w[51087693037816 60120172242323 60120174971147]
dhl_ecommerce_tracking_numbers.map do |tracking_code|
  t = TrackingNumber.new(tracking_code)
  t.valid?
end
=> [false, false, false]

Proposal

DHL eCommerce tracking numbers should pass validation.

Additional info

• DHL has many different pages for checking shipment status. For some reason, most of these pages don't recognize DHL eCommerce tracking numbers and none recognize them when they're freshly-generated. It seems eCommerce tracking numbers are not recognized until they're scanned. I've found this endpoint seems to be the most useful: https://www.dhl.com/us-en/home/tracking/tracking-parcel.html
• I have not been able to find any information about DHL tracking code format, checksum, etc.

[dan-jensen]

@jkeen this is an awesome gem, I've been using it for years. Thanks for maintaining it!

If you can point me in the right direction, I'd be happy to submit a PR.