Fix DHL Quotes for Domestic Shipments when Content Type is set to Non-Document

[gwharton]

Description (*)

1. Updated label for Content Type configuration field to make it clear what it is.
2. Changed Allowable Methods (Non Doc and Doc) to always be displayed no
   matter what the content type mode is. Makes no sense to display one or the other.
3. Changed the isDutiable function to only look at whether a shipment is
   domestic or not. Previously it would return dutiable for everything
   if the Content Type mode is non document (which causes problems for
   domestic shipments in Non Document mode). Fixes DHL Shipping Quotes fail for Domestic Shipments when Content Mode is "Non Documents" #19485

Fixed Issues (if relevant)

1. DHL Shipping Quotes fail for Domestic Shipments when Content Mode is "Non Documents" #19485:DHL Shipping Quotes fail for Domestic Shipments when Content Mode is "Non Documents"

Manual testing scenarios (*)

1. Set Shipment Source to UK, SW1 1AA
2. Setup DHL module to obtain online quotes
3. Set Content Type to "Non Document"
4. Obtain quotes for destinations
   4.1 UK, SW1 1AA (UK -> UK - Domestic - Documents - Non dutiable)
   4.2 FR, 75001 (UK -> EU - Domestic - Documents - Non dutiable)
   4.3 NO, 4032 (UK -> Europe - Intl - Non Documents - Dutiable)
   4.4 US, 90210 (UK -> World - Intl - Non Documents - Dutiable)
5. Ensure quotes are received for all of the above regions.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

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[magento-engcom-team]

Hi @orlangur, thank you for the review.
ENGCOM-3601 has been created to process this Pull Request

[ghost]

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