Use CustomersDot as SSOT for trial duration - part 3

What does this MR do and why?

Use CustomersDot as SSOT for trial duration

When we need to change trial duration, we end up making 2 changes that need to be coordinated in some way. The first on CustomersDot and the second on GitLab.com. We should try to avoid that as it creates a lot of friction.

This is the third part of the whole change.

References

Screenshots or screen recordings

Affected pages

How to set up and validate locally

• Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
• Create new group. Visit Settings -> Usage quotas.
• Make sure page loads. Visit Manage -> Members.
• Invite 4 random users. Make sure page loads.
• Visit /rails/mailers/namespaces/free_user_cap_mailer/over_limit_email.
• Make sure email has 60-day trial link.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #550781