Select Plan for Billing Page When Multiple Plans Have Same Code

What does this MR do?

We may receive multiple plans from CustomersDot with the same plan code. In this scenario, we may not select the correct plan from the list for display on the billing page.

This MR fixes this scenario so that we do select the correct plan. It is also tolerant of the new current_plan field missing in the response, so it should be deployable independently of the associated MR in CustomersDot.

Issue: https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/2598

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Testing this locally

See https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/2598#testing-this-locally

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team