Change duo pro trial duration to 60 days for in app messaging

What does this MR do and why?

Change duo pro trial duration to 60 days for in app messaging

• business decision
• see https://gitlab.com/gitlab-org/gitlab/-/issues/458848
• longterm plan for SSOT: https://gitlab.com/gitlab-org/gitlab/-/issues/455880#note_1887949196

MR acceptance checklist

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

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Before	After

How to set up and validate locally

bin/rails c

Feature.enable(:duo_pro_trials)

• Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
• Sign in. Create new group.

bin/rails c

GitlabSubscription.last.update(hosted_plan: Plan.find_by(name: 'ultimate'))

• Visit group's billing page. Make sure there is correct text in the card.

Related to #458848