Enable customers to be found by zuora_account_id under the admin path

Problem

We need a way to find the customer's account in the customers application from the version application.

Proposal

Use the Zuora account id that the version application has access to, and use that to find the proper customer account in the admin area of the customers application.

Result

Provides a linkable url for the version application to reference: https://customers.gitlab.com/admin/customer/:zuora_account_id

Next steps (if any)

Use this path in https://gitlab.com/gitlab-services/version-gitlab-com/issues/206

/cc @timhey