Feature/dimoco psp

[GilianJuice]

Describe your changes

Made some changes that are needed to implement a new PSP plugin (Dimoco). Changes are:

• Added Dimoco to PaymentServiceProviders enum.
• Made some constants for properties that were already used in the GCL, but also needed for Dimoco. I only converted some strings into constants, the rest we will have to do later because that's not in the scope of this project.
• Added possibility for saving a country code to basket/order, which can then be used in PSPs.
• Added XmlHelpers class with functions to serialize en deserialize XML.

Type of change

Please check only ONE option.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How was this tested?

I tested this in a customer project by making several test orders and debugging the code to see if everything is being handled correctly.

Checklist before requesting a review

• I have reviewed and tested my changes
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I selected develop as the base branch and not main, or the pull request is a hotfix that needs to be done directly on main
• I double checked all my changes and they contain no temporary test code, no code that is commented out and no changes that are not part of this branch
• I added new unit tests for my changes if applicable

Related pull requests

N/A

Link to Asana ticket

https://app.asana.com/0/1206726301569963/1206726303952348