Impact to SalesForce amendment opportunity creation with migration to Zuora's Orders API

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### Background

With https://gitlab.com/groups/gitlab-org/-/epics/6438, new subscription creation and amendment to existing subscriptions will be executed using Zuora's Orders API instead of Subscribe and Amend API.

After a subscription is created, an account in SalesForce is [created](https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/a0563d4d477684f0a49b56e57fff2eeb8ba8f469/app/services/subscription_manager_service.rb#L77).
After a subscription is amended, an opportunity is created in SalesForce ([source](https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/a0563d4d477684f0a49b56e57fff2eeb8ba8f469/app/services/self_service/subscriptions/update_service.rb#L57)).

When a subscription is amended, the [list of amendments](https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/a0563d4d477684f0a49b56e57fff2eeb8ba8f469/app/services/self_service/subscriptions/update_service.rb#L97) are sent to the opportunity creation service and the opportunity creation payload includes attributes that are [retrieved from the amendments](https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/a0563d4d477684f0a49b56e57fff2eeb8ba8f469/app/services/salesforce/create_quote_objects_service.rb#L104).

### Problem

Zuora's Orders API creates composite amendments, however they will [no longer be available once Orders harmonization is turned off](https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/4643#note_1079761771). (Orders harmonization lets the use of both Orders and Subscribe & Amend apis in parallel).

Thus, before rolling out the use of Orders API for amendment related actions, we need a way to determine:

  - [ ] does this change require updates to Amendment Quote (currently `sObject` is set to `zqu__QuoteAmendment__c` and result key to `quote_amendment_id`)? This requires input from `Sales Systems` team. 
        Please note this will also require a plan to support both types during the transition period from Amendment API to Orders API.

  - [ ] will this change involve updates to existing attributes or inclusion of any new attributes? This requires input from `Sales Systems` team. 

  - [x] determining the amendment related attributes that corresponds with Orders. Possible leads include using invoice line items / abstracting information from order actions. This requires input from `Fulfillment engineering` team. 

### Proposal

<!-- Consult with `@gitlab-com/business-technology/enterprise-apps/zuora-architects` on the ~"Enterprise Applications" team if Zuora business logic is involved. -->

TBD

### Result

Opportunity creation in SalesForce works seamlessly with the migration to Orders API.

### Next steps (if any)

### How will we measure success?

Story points: 3.0