[Testing] Upgrade subscription workflow using Orders API

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### Problem

This issue is to track the verification process to enable the use of 'Orders API in Subscription Upgrade workflow'.

**Associated FF:** [`use_orders_api_upgrade_workflow` ](https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/5050)

### Testing scenarios

<!-- Consult with `@gitlab-com/business-technology/enterprise-apps/zuora-architects` on the ~"Enterprise Applications" team if Zuora business logic is involved. -->

|Scenario|Steps|Expected result|Pass? (Staging environment)|Notes|
|---|---|---|---|---|
| SaaS - Upgrade Subscription from Premium to Ultimate from gitlab.com | 1. Create a group in gitlab.com <br/> 2. Purchase Premium subscription for the group <br/> 3. Navigate to the billing page of the group, and upgrade it to Ultimate. | Verify subscription is upgraded, SalesForce opportunity and objects created as expected | :white_check_mark: <br/> [Verification walkthrough](https://drive.google.com/file/d/13tkqZjfsUCFo98G0XUUlBEYLbvSTXrXe/view?usp=share_link) <br/> <br/> [Zuora subscription](https://test.zuora.com/apps/Subscription.do?method=view&id=8a8aa1b48461fe190184665b96f07eda) |  |
| Self Managed - Upgrade Subscription from Premium to Ultimate from gitlab.com | 1. Purchase Premium Self managed subscription in CustomersDot <br/> 3. Navigate to the subscription card, and upgrade it to Ultimate. | Verify subscription is upgraded, SalesForce opportunity and objects created as expected | :white_check_mark: <br/> [Verification walkthrough](https://drive.google.com/file/d/16pHEwfIxWBqkNfctEVpnuxYBKq0D1wTY/view?usp=share_link) <br/> <br/> [Zuora subscription](https://test.zuora.com/apps/Subscription.do?method=view&id=8a8aa13f8475790b018475c45c9a0834) |  |
| EoA Upgrade Subscription from Starter to Ultimate from gitlab.com (**seat limit not exceeded**) | 1. Purchase starter plan with seat limit less than 25 <br/> 2. Sign in to CustomersDor <br/> 3. Select subscription card, upgrade it to Premium. Verify discounted price shows up. | Verify subscription is upgraded with appropriate discount applied | :white_check_mark: <br/> [Verification walkthrough](https://drive.google.com/file/d/14aqBO6JWf4rCrSjZskvHCe6h4Bj6LAlw/view?usp=share_link) <br/> <br/> [Zuora subscription](https://test.zuora.com/apps/Subscription.do?method=view&id=8a8aa06b8475791c018476009a5f123d) |  |
| EoA Upgrade Subscription from Starter to Ultimate from gitlab.com (**seat limit exceeded**) | 1. Purchase starter plan with seat limit greater than 25 <br/> 2. Sign in to CustomersDor <br/> 3. Select subscription card, upgrade it to Ultimate. | Verify subscription is upgraded with **no** discount applied | :white_check_mark: <br/> <br/> [Verification walkthrough](https://drive.google.com/file/d/1z62e5J7hF8YuhIKE1LFY1mssaUfaIziy/view?usp=share_link) <br/> <br/> [Zuora subscription](https://test.zuora.com/apps/Subscription.do?method=view&id=8a8aa1e08475790b018475eedf720d8b) |  |
|SalesForce attribute verification| Upgrade subscription using any one of the above scenarios | - Creates `QuoteAmendment` for `RemoveProduct`, `AddProduct` <br/> -  Creates `QuoteRatePlan` for `RemoveProduct`, `AddProduct` <br/> - Creates `QuoteRatePlanCharge` for `AddProduct` <br/> <br/> [Comparison sheet](https://docs.google.com/spreadsheets/d/1ltJBcLwOau3-95CuHCwlXiZP200XkCqdeKtdpoYNUBI/edit#gid=0) | :white_check_mark: [SalesForce Quote](https://gitlab--staging.sandbox.my.salesforce.com/a1d740000011D5p) |



### Result

### Next steps (if any)

### How will we measure success?

Story points: 3.0