Move Confirm Order API call from store to component

What does this MR do and why?

Move Confirm Order API call from store to component in new subscription purchase flow.

• No functionality or UI changes, purely a refactor

Related to #427094 (closed)

Screenshots or screen recordings

Scenario	Screenshot
Successful purchase	Screenshot Success Subscription created - https://apisandbox.zuora.com/platform/subscriptions/8ad083528adb8ef3018af410337769f1
Successful purchase with new group creation	Screenshot Screen_Recording_2023-10-04_at_10.14.14_AM Subscription created - https://apisandbox.zuora.com/platform/subscriptions/8ad093fb8adba1d9018af76452b878d9
Successful purchase as a new user	Screenshot Screen_Recording_2023-10-04_at_10.56.09_AM Subscription created - https://apisandbox.zuora.com/platform/subscriptions/8ad087d28adb8ef3018af78aa40d115fhttps://apisandbox.zuora.com/platform/subscriptions/8ad093fb8adba1d9018af76452b878d9
Email already taken error (with error attribute)	Screenshot
Server error (caught in catch block)	Screenshot
Error response with name key	Screenshot
Invalid promo code error	Screenshot
Loading state while confirming	Screenshot

How to set up and validate locally

Application setup

1. Customers Dot needs to be setup in order to view the billing page for a group
2. Start GDK in SaaS mode GITLAB_SIMULATE_SAAS=1 gdk start

Subscription purchase

1. Create a Group
2. Go to Settings > Billing
3. Click on Upgrade CTA

Error scenarios

1. Email already taken
   • Unlink GitLab sign in for a customer on Customers Dot and sign in with that customer's email id on GitLab.com
   • (or) Update create method here to be:

     def create
       render json: {
         error_attribute_map: { email: ["taken"] },
         errors: "Email has already been taken"
       }
     end

2. Promo code invalid
   • Update create method here to be:

     def create
       render json: {
         errors: {
           message: 'Promo code is invalid',
           attributes: ['promo_code'],
           code: 'INVALID',
         }
       }
     end

3. Response with name attribute
   • Update create method here to be:

     def create
       render json: { name: ['Error_1', "Error ' 2"] }
     end

4. 404 error when group not found
   • Update this line to be return not_found

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.