New Trial flow for logged in user should not take them to the Customer Portal
### Summary
A user should not have to interact with the Customers Portal when starting a new Trial. There has been a new flow created to handle this user flow https://gitlab.com/gitlab-org/gitlab/issues/13233.
### Steps to reproduce
1. Logging into GitLab
1. Create a group
1. Selecting `Start free trial` from within a group billing page
### What is the current *bug* behavior?
https://www.loom.com/share/e13df17607d441b9b0b1b568eb543721
### What is the expected *correct* behavior?
A logged-in user should be taken to the new Trial flow.

### Relevant logs and/or screenshots

cc @rhardarson @chris_baus @tipyn @aalakkad @vitallium @jameslopez @asubramanian1 @s_awezec @a_akgun
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