Draft: Use full regex for free trial redirect to fix review apps

Why is this change being made?

This MR might fix gitlab-com/marketing/digital-experience/buyer-experience#744 (comment 955200088) by using the more complex regular expression matching on the free trial redirects. It needs to meet the following criteria:

1. /free-trial/index.html should redirect to /free-trial/
2. /free-trial/index.html/ should redirect to /free-trial/
3. /free-trial/index.html?return_to=https%3A%2F%2Fgitlab.example.org should redirect to /free-trial/?return_to=https%3A%2F%2Fgitlab.example.org
4. /free-trial/index.html/?return_to=https%3A%2F%2Fgitlab.example.org should redirect to /free-trial/?return_to=https%3A%2F%2Fgitlab.example.org
5. /free-trial should continue to redirect to /free-trial/
6. The JS should load correctly on all of the redirected targets (it wasn't for 3 and 4 in a previous iteration, until we used the literal regex to match.
7. Review apps and production should work precisely the same.

I am going to verify this by following the testing workflow and see if things work out. Fingers crossed!

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