Fix Trial starting end up on 404 page

What does this MR do and why?

• Resolves the page specific javascript issue when select template is rendered instead of new on a failed create_lead
  • details in #393760 (closed)
• Adds further test coverage

Screenshots or screen recordings

most conditions can be seen in the feature spec coverage added in this MR - hard to reproduce unless faking errors from customersDot locally

How to set up and validate locally

most conditions can be seen in the feature spec coverage added in this MR - hard to reproduce unless faking errors from customersDot locally

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #393760 (closed)