Add can apply to promotions

[mamhoff]

Summary

This fixes the orders/adjustment pages when using the new promotion system.

Bug report from @boomer196 on Slack:

Using Solidus v4.4.1 and I have the “new” promotions installed (no legacy). When I click on the Adjustments tab of an order and it blows up.
The app/views/spree/admin/adjustments/index.html.erb in solidus_backend has a check to see if it should display the coupon code section:

<% if @order.can_add_coupon? && can?(:update, @order) %>
  <div data-hook="adjustments_new_coupon_code">
    <%= text_field_tag "coupon_code", "", placeholder: t('spree.coupon_code') %>
    <%= button_tag t('spree.add_coupon_code'), id: "add_coupon_code", class: 'btn btn-primary' %>
  </div>
<% end %>

app/models/spree/order.rb has a method called can_add_coupon? and it tries to call can_apply? on the Spree::Config.promotions.coupon_code_handler_class

def can_add_coupon?
  Spree::Config.promotions.coupon_code_handler_class.new(self).can_apply?
end

ActionView::Template::Error (undefined method `can_apply?' for an instance of SolidusPromotions::PromotionHandler::Coupon):

Causes:
NoMethodError (undefined method `can_apply?' for an instance of SolidusPromotions::PromotionHandler::Coupon)

[kennyadsl]

👌 everything here makes sense, thanks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.46%. Comparing base (d0ccd7e) to head (3588c15).
Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6013      +/-   ##
==========================================
+ Coverage   87.81%   89.46%   +1.64%     
==========================================
  Files         476      782     +306     
  Lines       11658    18009    +6351     
==========================================
+ Hits        10238    16112    +5874     
- Misses       1420     1897     +477     

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[mamhoff]

Not sure what happened to the Backport PR? I don't see it?

[kennyadsl]

I tried to retrigger the flow but it's still skipping it. I don't think we changed anything there recently, so it might a temporary issue with GitHub Actions.

[tvdeyen]

Should be fixed by #6016

[github-actions]

💚 All backports created successfully

Status	Branch	Result
✅	v4.4

Questions ?

Please refer to the Backport tool documentation and see the Github Action logs for details