Resolve "[ENG] Duo pro flows: Consolidate duo-pro/sales with duo-pro/sales"

Build Variables:

• Use Contentful Preview API

🛑 Publish before merging:

1. https://app.contentful.com/spaces/xz1dnu24egyd/entries/3RYF8IZOrT5OWmCnUpdcqm?focusedField=internalName
2. https://app.contentful.com/spaces/xz1dnu24egyd/environments/master/entries/3y4FggPEN1gmiWhl6bkYpL?focusedField=internalName
3. https://app.contentful.com/spaces/xz1dnu24egyd/environments/master/entries/3uwIEJT93Q7DMkDGYrZgnM?focusedField=internalName
4. https://app.contentful.com/spaces/xz1dnu24egyd/environments/master/entries/2W0uVTKpIX3Z1dHKC2WtiS?previousEntries=4G41hUowMzddDyxVnn7gsB
5. https://app.contentful.com/spaces/xz1dnu24egyd/environments/master/entries/7nCMPwQcJQeV5QTcaaD3ut

🛑 If #3707 (closed) is merged before, rebase and re-update. Otherwise inform @mduque-ext about the link removals

Changes in this MR

1. Deleted /solutions/gitlab-duo-pro/self-managed-and-gitlab-dedicated-trial/
2. Consolidated all GitLab Duo free trial workflows into a single source on /solutions/gitlab-duo-pro/sales
3. Updated /gitlab-duo Free trial links to go to the consolidated sales page + Deleted the free trial section
4. Updating GitLab Duo card - removing a few CTA buttons to consolidate into a single 'Try for 60 days' cta: https://3818-eng-duo-pro-flows-consolidate-duo-pro-sales-with-duo-pro-s.about.gitlab-review.app/pricing/

Notes:

1. The forms successfully fire the correct dataLayer events on submit. On submit success, the page state changes into a 'Thank you for submitting' visual
2. A certain tab can be opened by default, allowing the correct tab OR form to show on page load. No URL parameter will show the free-trial tab open by default. If the page visitor has ?type=free-trial in the URL, it will still be selected by default AND the form will be opened. The ?type=contact-sales param will open the other tab, showing that specific form.

Related #3818 (closed)