Draft: Show the link to CDot on DuoPro page for SM

What does this MR do and why?

Instead of Contact sales button show the link to Customers Portal purchase flow for SelfManaged instances Duo Pro page

Related to https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/8219

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.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Customers Dot needs to be setup
2. Start GDK in SM mode GITLAB_SIMULATE_SAAS=0 gdk start

Subscription setup

Note: you might have done it before, check your Admin Area first

1. Buy Self-Managed Ultimate 1 Year subscription on Zuora Sandbox
2. Copy the license key from the subscription details page on local Customers Dot instance
3. Paste the license key on your SM instance at Admin Area > Settings > General > Add license
4. Refresh the page to see the Code Suggestions Menu item appear under Admin Area

When all of the above done

1. Login as admin
2. Reach admin/code_suggestions page